How much money to budge?

Do not try to get forints before your trip. Just use an ATM in Budapest, being sure not to have the withdrawal recorded in dollars. I did not find a bank-owned ATM at the Budapest airport last month, so I mentally crossed my fingers and used the only one I did see, which was the not-usually-recommended Euronet. I'm still traveling and don't know how that transaction was recorded when it hit my credit union account, but there was no indication of a problem at the ATM itself. I was taking a cheap public bus (100E) into the city and walking from Deak Ferenc ter to my hotel, so I withdrew a very small amount of money (about $20 worth) just in case there turned out to be some funny business with the exchange rate at that ATM, but I believe all was OK.

Your back-up plan can be having a modest amount of nice, crisp US currency available in case you need to use the staffed exchange booth at the airport. That will most definitely cost you extra, but it's unlikely that you'll need to employ that back-up plan.

Tip: When you get to a bank-owned ATM and are ready to make a larger withdrawal, be aware that many Hungarian ATMs dispense the largest bills possible to meet your withdrawal amount. If you request Ft 20,000 (which is about US $80), the ATM may well give you one 20,000-forint note. Good luck trying to spend that. Obviously, you need to be aware of any ATM fees your bank is going to charge you, but otherwise, it's better to stick to small withdrawals so you get more-usable currency.

As always, switch the language to English on the ATM, watch for notifications of fees to be charged by the ATM itself (just cancel the transaction, retrieve your card and find a different bank's ATM), and do not let the machine record the transaction in dollars.

You should be able to use your credit card (assuming it's Mastercard or Visa) for nearly all non-trivial purchases in Budapest, but just as at the ATM, be sure the transaction is denominated in forints rather than dollars. Pay attention to what is happening with the card-reader. I had a problem elsewhere in Hungary with restaurant personnel taking it upon themselves to switch the currency to dollars, and that is a very bad thing, because they get to choose what (definitely not good) exchange rate you get.

As for how much money you'll need, I'm not a great judge of that. Individual tickets for local public transportation are Ft 350 (close to $1.50) if bought from vending machines (I used cash and don't know whether they take credit cards); I think it's Ft 400 or 450 if you pay the bus driver directly, and that would require cash. If you decide a Budapest Card is worthwhile, that will cover your city transportation (not the airport express bus I used), and you can buy the BC via credit card. My usual practice is to pay for small puchases, including low-cost museums, in cash, so I don't know what would happen if you wanted to pay a Ft 1000 admission fee with a card. The major museums seemed to take cards.

You do not want to over-withdraw forints, because they are not usable outside Hungary and converting leftovers to dollars at an exchange booth would be very costly. (Worst case, don't wait till you get back to the airport for that conversion.) I wouldn't try to guess the total you're likely to spend in forints; I'd just withdraw a modest amount and plan to hit another ATM if I needed to.

My beverage of choice is bottled water, and I had nice meals in solid, not-fancy restaurants for mostly not more than Ft 5500. Only once did I pay more, and it was still less than Ft 7000. Again, that's without alcohol or coffee, and usually without dessert. Note that many people would find it difficult to sit down to two full Hungarian restaurant meals in one day. But do watch out for sneaky servers trying to charge you in dollars. And take a look at the menu and (especially) the check to see whether a service charge has already been included.

Now that I've checked your posting history, I see that you probably are already aware of the warnings I included in my earlier response. Sorry about the unnecessary rehash of stuff you already know.

There is a transportation desk for shuttles to your hotel out in the airport concourse. You can charge your van trip on a credit card and wait until you get into the city to find a bank ATM. I have noticed the city has a bunch of nonbank ATMs in heavy tourist areas.

Thanks a lot acraven and David. I will note down
Your advices.

I prefer to use OTP bank whenever possible for cash withdrawals, also used Euronet this past trip and had no unusual fees tacked on besides the $5.00 non-Chase ATM fee at both. I travel solo so I bring some forints with me, usually around 30,000 (about $110 US). Worth it to me for the peace of mind, that way I can start enjoying Budapest without worrying about finding an ATM immediately. While I do use my credit card for most purchases, I also go to the flea market and cash is preferred especially if you're going to haggle :) If you attend any festivals you will need cash for food, drink and any purchases--at least that's been my experience attending 5 events over my past few visits.

One thing to watch out for when getting change--Hungary replaced some of their currency with new versions and I got a 2000 HUF note from a liquor store that was unusable. No big deal, about $7.00 US.
https://dailynewshungary.com/wp-content/uploads/2016/10/IMG_20161015_083130-1280x640.jpg

Christa's note about the old 2000-forint note reminded me that I was given a smaller bill with a small bit missing at a corner. Two different people threw up their hands in horror when I tried to spend that bill. I don't think there's anything wrong with a slightly damaged bill like that; a server in a restaurant was happy to accept it. However, on a short trip you don't want to get stuck with a large bill that may be hard to get rid of, so watch the condition of the bills you get in change.

If you get stuck with the old bills you can go to any bank and change them. You will need your passport.
In the tourist zone the 20.000ft note will not be an issue to spend.

I would suggest you pull from an ATM 50.000 forints ($180). Use the 20's for a couple of small purchases in the tourist zone so you have small change, then use your credit card when ever possible. If you run out of forints, just stop at another ATM. They are all over the place. Most are inside locked rooms, but any card with a magnetic strip will unlock the room

Other than that i can not imagine how much you will spend. Depends on what you do when you travel and in what part of town you do it in.

Rather than messing with metro tickets get a TravelCard for the length of time you will be there. Its the cheapest and by far the easiest way to get around.

For food costs, look at some menus

EXCELLENT HUNG / JEWISH ($$)
MACESZ HUSZÁR
District VII, Dob street 26.
+36 1 787 6164
www.maceszhuszar.hu

ALL YOU CAN EAT HUNGARIAN ($$$)
TRÓFEA GRILL
District VI, Kiraly utca. 30-32.
+36 1 878 0522
http://kiraly.trofeagrill.eu/

GOOD GYPSY MUSIC / FOOD ($$$)
RÉZKAKAS BISTRO
District V, Sas utca 3
+36 1 318-0038
http://www.rezkakasbistro.hu

IF CHILI’S OPENED A HUNGARIAN RESTAURANT ($$)
VAKVARJÚ ÉTTEREM
District VI, Paulay Ede utca 7
+ 36 1 268 08 88
www.vakvarju.com/

I NEED! A HAMBURGER . ($)
ZING BURGER
District VI, Kiraly Utca 60

OLD WORLD HUNGARIAN FOOD AND ATMOSPHERE ($$)
PAPRIKA ÉTTEREM
District VII, Dózsa György út 72
+36-20-294-79-44
http://www.paprikavendeglo.hu/

NEW IN-PLACE IN TOWN ($$)
HUNGARIKUM BISTRO
District V, Steindl Imre u. 13.
+36 30 661 6244
http://hungarikumbisztro.hu

GOOD HUNGARIAN FOOD ($$)
BELVÁROSI LUGAS
VENDÉGLŐ
District VI, Bajcsy Zsilinszky u.15
+36 1 302 5393
http://lugas-etterem.com/

MY FAVORITE WINE BAR HAS GREAT FOOD. 150 FEET FROM THE APT ($$)
KADARKA BÁR
District VI, Király utca 42
+36 1 266 5094

GOOD BREAKFAST ($$)
CAFÉ VIAN
District VII, Király u. 13
+36 1 878 1350

SWORD FIGHTS & BELLY
DANCERS & GREAT FOOD ($$)
SIR LANCELOT
District VI, Podmaniczky u. 14
www.sirlancelot.hu
+36 1 302 4456

GOOD CHEAP HUNGARIAN ($)
FRICI PAPA KIFŐZDÉJE
District VI, Király u. 55
http://www.fricipapa.hu
+36 1 351 0197

Thanks for all your detailed response. I might get an equivalent of $100 in forints here before I leave and get the rest from ATM there.