We are traveling SEA to AMS and out of CDG in April on Delta non stops. We bought at $850 in November when the price was not moving. Today when checking the load I saw it dropped almost $200 less. If you’re thinking about it from the West Coast now might be a good time to buy.
Seattle to European continent for $650 round trip in spring? Which airline, please. I never heard of a price that low. Are you sure you were looking at live pricing by reliable sites?
On kayak.com, many flights on KLM/Delta starting at $705 round trip SEA - AMS. Pretty great! Other airlines, like British Air/American and United/Lufthansa at about $70 more.
On Delta directly through their site. Right now basic economy is $654 rt for April 10-26 as an example.
Heads up on 'basic economy'. It is the most restrictive; nothing is allowed in the overhead compartment. Your carry on and coat must be slim enough to fit under the seat in front of you.
Delta's basic economy rules allow a full size carry on- you're just boarding last and may or may not have to gate check it for lack of room. American and United's basic economy are the ones who don't allow a full-sized carry-on.
If you have Delta's American Express credit card, you still get your free bag benefit when you buy a transatlantic BE ticket. (Annual fee on the Gold card- $95; checking a bag there and back with a BE fare- $120)