In the 70's you I was able to fly JFK to Paris for around $250 RT on airlines like Tower Air.
Nathan's is currently running a buy one HD for full price get a seond one for $0.05--using the "hidden city" flying model, I'd just buy the SECOND HD.
In the late 1990s and early 2000s, I was flying between the U.S. and London for $280-350 roundtrip on AA, UA, BA and other carriers. The benefit of there being more planes and larger planes and more competition.