Don’t wait on this deal — I’m seeing flights priced from NYC/EWR to destinations in Europe (Paris, Amsterdam, Rome) for around $300 with October - April availability. A stopover in London or Helsinki will cost you a bit more, around $330.
This deal, which the good folks at The Flight Deal say isn’t a mistake fare, is an American Airlines basic economy deal. With basic economy, you are limited to one personal item and one carry-on, ineligible for upgrades,
If you can deal with those restrictions, this is a pretty good deal as flights to Europe at this time of the year can often cost $800 or more. Play around with the dates below and see what you come up with. But don’t wait, this is unlikely to last long.