Maybe I should have put my $200 somewhere else . . .
I would suggest when you think it's time to upgrade look for nothing older than a (used) MacBook Core 2 Duo model. Things may change in the future, but that would be my recommendation as I post this.
When buying a used Mac, always buy one that includes the original software discs (Install and Restore, sometimes on a single DVD), and also any upgrade media for the version to which the Mac has been upgraded.