The Persona series of games are probably the most readily available - if you can't find them locally Amazon should have them at a decent enough price. Persona 3 FES new should run $20ish and Persona 4 around $30-40. Most other games in the SMT line just don't seem to be as popular and seem to be much harder to find, so you'd probably have to go the used game route to get them and even then they may still be somewhat costly.
I'd just start with whatever one you can find first. I think playing Persona 4 first may put you off to some of the aspects of P3's battle system but honestly they're both good enough games that if you can't get through P3 after playing P4 it's really just your loss not mine or Manny Ramirez's.
He was suspended 50 games.
