Oh jeez what's wrong with it/how much of a rebuild are you talking?
Not to be a constant rain on parade, but things that you mentioned like air filter cause a negligible difference in power. When I say negligible I mean that if you had a 330 with full CAI, crazy spark plugs, cat-back-- the normal start-off mods-- next to a bone stock one, it would be nearly impossible to feel a difference in power. Even on a drag strip or dyno were still talking minimal if any gains. And all those mods would be between 500-1000 bucks. Sucks, I know.
IMHO and experience, the more worthwhile "mods" on budget are things you'll ACTUALLY notice while driving rather than trying to focus on going faster. Things like weighted shift knobs or deleting the CDV, tint, stereo upgrades, wheels, mild exhaust, and even preventative maintenance like SS braided brake lines if yours looks bad quality, or stiffer suspension bushings should they need to be replaced.
Budget wise, the lowest you'll pay for a noticeable power gain would be over $1000 for cams and a tune with supporting intake and exhaust. Again, IMO that 1000 bucks would be better spent on two HPDE sessions learning how to actually go faster, or on nice wheels you'll constantly smile at, or a dynavin, or a really good lap dance... You get my point :p
Just my $0.02
ps if you do want a nice filter, there's a lifetime K/N one on sale here currently in the FS section.