Bank Fees

If you have a debit card with no ATM fees or foreign transaction fees, there will be no cost.

Many banks will not exchange your cash. You will have to rely on exchange bureaus , and rates will vary.

Most sensible plan is to use your atm card to withdraw euros.

If, and that is a big if, if the bank is willing to exchange money it will run in the range of 10% or more. But more likely they will not do the exchange because that is not their business. In the same manner as someone from Europe walking into your local bank to exchange Euro for dollars. The cheapest and most convenient way to obtain local currency will also be using a debit card at a bank own ATM anywhere in Europe. Even if your card issuer adds fees it will still be cheaper than exchange bureaus in Europe. Use a debit card, only sensible way to go. Also, pre-paid debit cards can be a trap.

An exchange bureau may advertise "No Fees" but they will make still make money by offering a poor exchange rate - mostly in the range of 10 to 15% less.

I agree that using an ATM is the best. According to this article it's usually 7% if you do the exchange in the post office or a major bank, vs 15% at a currency exchange place: https://www.ricksteves.com/travel-tips/money/cash-tips

My experience in Italy is that banks will not exchange currency for you unless you have an account with them.

Debit cards are the answer - I prefer to use them at bank-connected machines during business hours.

Just use an ATM card and be done with it!

or shop around amongst the many bureau du change in every major European destination

That is a waste of time. First, while exchange bureaus can be found in major European cities they are not that frequently and often hard to find. But banks and ATMs are far more frequent and will always be cheaper and more convenient. About the only differences between exchange bureaus is how they collect their fee for changing your money and not in the amount of fees.

When I was in Paris a week ago, I happened to walk by a travel-ex exchange window and exchange rate was $1: to 0.80€. The rate received at ATMs for my trip was about 0.915€ to $1.

Only exchange dollars if all else fails.

That is a good example. That is a difference of nearly 15%. On Dec 15 the exchange rate was 1.086. The networks add about 1% or about a penny to the exchange rate so the rate was $1.09 to $1.10. A .80 Euro is $1.25 at the exchange bureau. So you can see that the exchange bureau is burying about 15% fee in their exchange rate. It is called a sucker play.

Karen's Paris FX kiosk example is less a "sucker play" and more an example of free enterprise cost of convenience. These tourist (an airport) FX kiosks typically show bid/ask prices. Tourist are free to exchange or not exchange their currency.

I'll carry some US currency to exchange in an emergency but I rely on bank ATM's. The charge is only what your bank charges you, which can be a low of nothing (special investment accounts or other offsetting deposit requirements) to as high as a flat fee (up to $5) plus a foreign exchange fee (3 percent is the highest I know of). So the highest charge, for $100, from an ATM would be nothing on the Europe side and $8 from your bank. My bank is USAA, they charge a flat exchange fee of one percent - $1 for a $100 withdrawal - which I think is reasonable. Many credit unions charge the same. If you're bank charges too much, consider opening a travel account and bring your regular ATM/Debit card as an emergency backup.

Here's some things to know:
1. Avoid exchange booths that look like an ATM. I've seen Travelex machines popping up in airports, they look like ATM's but charge you like an exchange booth. Stick to machines that have some form of "Bank" (e.g.Banco, Banc, Bank of) in the name and avoid any with "Ex" in the name. If I see a machine called "Bankex" I'll find another 50 meters further.
2. You need a card with a 4 digit PIN that is a number (or know the number of the letters you normally use). The number pads in Europe won't have letters on them.
3. Let your bank know you are going. It's a good idea to call customer service more than once to confirm they know. If not, you're card will likely get a fraud warning the first time you use it. It will be locked until you call the bank, then clear overnight, leaving you potentially cashless.
4. Fraud relating to ATMs use something to magnetically record your card PLUS something or someone recording you entering your PIN. Lots of machines have a warning screen that suggest you cover the hand you enter your PIN with your other hand so no one - not even a tiny camera attached to the machine above the pad - can see the number you enter.
5. This type of fraud requires accessing the machine when no one is watching. I think it's safest to use indoor machines (bank lobby, grocery store, department store, TI, etc.) because they are always in plain view of people and difficult to tamper with. Some bank ATM's are in a locked glass enclosed room, again for your safety, usually swiping your card in the lock will open the door.
6. Every card has a daily cash withdrawal limit, for your protection. A few banks will let you adjust your limit, most won't. Know your card's limit and when your card refreshes (normally midnight at home). You may end up making two withdrawals that seem like two different days but, because of time differences, are affected by your daily limit.
7. European machines often have a separate transaction limit that has nothing to do with your bank's daily limit. Many machines might limit you to 150 to 250 euros per transaction. Try more than one smaller transaction (hopefully with a bank account that doesn't charge you a per transaction fee) or try another machine. I barely remember having had a problem with an ATM because there's always a few more less than a block away if one doesn't want to work.
8. Any time a machine, waiter, hotel asks if you want to charge in local currency or U.S. dollars, the answer is always local currency. If you choose dollars, you will pay a currency exchange fee and your bank will still charge their full fees.

If what you are exchanging is only $100 and that is all you will exchange, then just go to any exchange bureau. The rate will be lousy but for that small amount it won't be anything that will ruin your trip. If all we are talking about is $100. After that just go to the ATM .

The currency exchange business has really dried up since the euro came out in 2002 and also in that time, we see much more widespread acceptance of credit and debit cards for payment. In most cases, the only banks that would do currency exchange for non-account holders are at airports and major train stations. Even currency exchange kiosks are much harder to find and their rates are all horrid. As an example, in central Rome recently in peak tourist season, I saw only three currency exchanges open and none had customers. Perhaps because the rate they offered was 10-20% worse than ATM or just paying with Visa or MC?

Another potential option - although I agree with all the others who recommend having and using a cash-withdrawal debit card at an ATM (called Bancomat in Spain and Italy), so I wouldn't personally do it - but your departure airport in the USA will likely have an exchange bureau window, and you could just get on the plane with some freshly exchanged euros. They may or may not give you a worse deal in fees and exchange rate than you'd get in Europe, but it might work for you.

Travelex offers a multi-currency reloadable debit MasterCard with chip and pin called a cash passport. I have used this in Europe and Australia at ATM's to withdraw the local currency and also used it to pay at restaurants and shops with no problems at all. You can load this card with USD before your trip and use the ATM to get the local currency when you get there. There is a $2.50 withdrawal fee per ATM transaction so make a larger withdrawal rather than several smaller ones to save on the fees.

Travelex is just about the worst investment every devised. According to their website, to load the card today with 1000€ would cost $1217.73. The current Interbank rate is $1084.50 per 1000€. That's a conversion charge of over 12%. Apparently, if you load the card in $US, the exchange rate discount is only 5½% plus a fee, still almost twice the worst rate from a US debit card. The worst rate from an ATM with a US ATM or debit card is about 4% (3% plus $5/$500 fee. To put it another way, using the Cash Passport card instead of you bank ATM card for 1000€ will cost you over $133.

And, if you have any money left on the card, it will cost you $20 to get it back.

The "free enterprise cost of convenience" = "sucker play".