Since people are adding prices, I will add this info about the posts above.
In late fall 2021 I paid $476 for Philadelphia-Edinburgh and Dublin-Philadelphia for April 2022 in basic economy on American. In March of 2022 I paid $312 (!) for Newark-London and Dublin Philadelphia on American in coach, and additional seat for this flight purchased in July cost $483 (long unfortunate story, but getting the AA Mastercard ate up $400 of this via cashback).
Just booked a flight to London for May that also now includes Iceland stopover to visit son and d.i.l. If not doing Iceland, the London trip would be $773 from Philadelphia, or $680 to go from Newark and return here, again on American in coach. If bought through BA (as first flight could be codeshare) would be even more as their seat purchase fees are, and always have been, way more than AAs. FWIW, via Icelandair this Newark to London roundtrip with stopover was $421 in Economy lite, seats still made this less than economy standard. Plus about $15 each way to get between here and Newark, which is surface transit and has nothing to do with the airlines.