The best cheap US PS1 game that has aged well is probably Gundam Battle Assault 2. I see it for less than $10 all the time.
This. great game, loads of fun, and still holds up today.
other than that, i'd say the final fantasy series, Spyro, Crash Bandicoot, persona 2 (though you can get the remake on psp), and the mega man legends games.
though, there are a lot of sprite-based rpgs, those are usually at least decent.