Personally I really like the b&w Japanese versions, the UraTama and EnTama, though they are very different from the v4 and v4.5, so if you buy one of them don't expect them to be a replacement of the other!
I'm currently enjoying the M!X, I also am quite a fan of P's, but when it comes to cheaper non-colors, v3's and Music Star are really fun, look around if you can find one for cheap.
[Offtopic] Also, thank you for your concern. My depression should get at least slightly better if I finally pass my math final and move on to college (failed math final is preventing me from graduating), because then I won't be that much under pressure.