He probably moves like 80 posts a day, or at least it seems lately.
If you're staying N/A,
2.5 Off road Down pipe (or one with cat if you so choose) $150 - 250
Power Log $100 - 200
HV3 $200
Intake $ 40 - 350
Rockers $300 - 550
Tuned PCM(after more than 1 of above) $100 - 200
In my car(when it was NA) the Downpipe made the biggest difference to be honest, followed by the PCM which made better use of my intake and exhaust work.
I said Top swap was out of the question when I started too.........