One Way Flight:Skyteam

However, when I click on the search, Delta has that flight listed for
over 2,000 Euros and it says that I'd need to book through KLM or Air
France...even though Google indicates it is marked also as a DL
flight.

Do all the flights involved have Delta flightnumber? If one of the flights are not in the Delta system, I'm not surprised that Delta can't sell you the ticket.

And, why does the Delta website have it in Euros and not USD?

It's not uncommon for airline websites to sell their tickets in the currency of the departing airport.

This might make using the vouchers complicated or impossible, but all cruise lines have an air departments which have contracts for discount flights. Not always the best deals, they're very well priced for one-ways.

So your problem is the cheap fares that you are seeing are not released to Delta by their partner airlines. The partnership doesn’t mean everyone gets every airfare.

This is a case where you may need to book using a Delta agent. One-way tickets can be much more per segment than round trip.

FYI: The ticket I booked was more expensive on the Air France website, so I booked through Delta.

bbr---

I don't know what your Florida city is, but I looked up one-way flights LIS-MCO and MCO-LIS (MCO=Orlando) on a random day in May. The MCO to LIS flight is $904; in the opposite direction, it is >2000 euro. I wonder if this is the pricing algorithm Delta has set up for the US not being open to Europeans. It's almost like the website is assuming you are a European trying to travel to the US. Since the only Europeans allowed into the US right now are business people, it would appear Delta is... uhh... gouging the business crowd. That pricing structure is in place in Sept 2020, too. I checked my city in SC -- same thing in Sept 2020 and May 2021.

I checked the KLM website for MCO-LIS and LIS-MCO on the same May date. $929 MCO-LIS; $429 LIS-MCO when I enter myself as buying in US. Similar prices in pounds/euros if I enter myself from the UK or Portugal.

As much as I hate to recommend this given Delta's current staffing issues, I would think about calling the reservation desk to check to see if the website is giving the fare for a European citizen buying a ticket in Europe. There may be a different fare for a US citizen buying the same ticket from the US (priced in US dollars). You can also try Twitter or a message through Facebook. Waits tend to be shorter late in the week (Thursday, Friday) -- the farther you get past "Schedule Change Saturday," the better.

i saved you a call to Delta. I called the Diamond Medallion line and got through immediately (maybe there weren't many changes this Saturday?). The >2000 euro fare is indeed the fare for LIS to MCO in May. When the customer service rep pulled it up (after checking the MCO to LIS flight), his exact words were, "Wow. That's crazy." (As an aside, I checked the one-way airfare on a Berlin flight to my local airport two weeks ago, and the cost was similar.)

I knew Delta would not match another SkyTeam fare, but the worse they could do was say "no," right? The customer service rep said no.

I think Delta is saying, "We don't want to do one-way flights from Europe to the US."

Do you need to buy your flight 10 months in advance? I know you have credits and things to use, but prices and availability may change again.
Alternatively even though it may not change overall price much, what about separate tickets such as Lisbon to New York area and then from there home?
Personally I would wait, checking weekly? Monthly?
Alternatively, if considerably cheaper, you buy return and not use the the return flight to Lisbon

Use Kayak.com for cheap flights.

MariaF brought up a good point. I didn't think to check round trip. It's around 700 euro (main cabin) with outgoing departure from LIS on same day with a return one week later. I checked on United and American... same fare structures... super high one way price and much cheaper round trip. So... it's a thing US airlines do.

I did a little more digging around (I'm curious about these things!) and found that the US airlines indeed are betting that one-way travelers from Europe to the US are business travelers and have built a really big premium into these airfares. They apparently are willing to lose the low-fare one-way leisure traveler to someone else in order to maintain the premium on one-way business travel. If you are interested in reading more about this, see the blog post regarding this from Brett Snyder aka Cranky Flyer who previously worked for United and now owns a travel agency: https://crankyflier.com/2018/02/08/why-are-one-way-fares-so-expensive-internationally-ask-cranky/

So, unless the US airlines change their policy on one-way tickets from Europe in the next several months, it is unlikely you are going to find an inexpensive one-way LIS to Florida flight on Delta.

As far as buying the round trip and not using the return flight, there is some risk with that. If you call to cancel the flight, I expect the contract of carriage gives the airline the option of re-calculating your airfare to a one-way ticket. I expect the same if you don't show up for the return flight. I don't think this would happen for one instance, but the airline could cancel your frequent flyer account or even put you on a no-fly list. A few years ago, Lufthansa sued a guy for the airfare difference between purchased and flown itineraries due to him repeatedly skirting airfare rules by no-showing for flights (either second leg or return flights).

Yes, Dave, you are correct in that there is a risk in buying the return and not using it. Rather than cancel the 'return' when they may recalculate the rate, you can be a 'no show', which means then you are just an inconvenience to all.
It isn't something I would do, but it is what has happened.

Repeat offenders certainly find themselves with repercussions.

I did a test booking Lisbon to Miami mid May. I use MatrixITA software for planning my travel. Rather ludicrous. TAP and Turkish Air will fly you for 5-620E and everything else, 1900E and up...except something called Air Europa for 1400E
If you try to fly from Porto, Portugal, TAP fare drops to under 300E to Miami but everything else is the same high price.
Madrid to MIA is 1164E on Delta.
Lisbon to JFK or Toronto are also up there.
Looks like options are either wait for some price drops, or change airline expectations.
(In the past, I looked at transatlantic cruises. Multi country tickets were pricey, and 2 one ways were the way to go. Not sure that will be the case moving forward).

Given everything that has been posted, I'd contact the cruise line to see what they can do. I've read that they often can arrange decent one-way fares in conjunction with repositioning cruises.