Yeah, are we talking the easiest mods, the best cost versus benefit, or the ones that result in the biggest increase in power?

If your not a rich slub (such as myself) and your modding as money is available, then a CAI is #1. It's a bang for your buck thing. For $20-$?0 dollars its an inexpensive mod that you can definatly feel. 8)

CAI
TB
LIM porting
S/C porting
CH porting
PEM's
HF CAT
CAM
PISTONS
ELECTRIC WATER PUMP

A half-decent CAI is going to cost a bit more than $20. You can't buy either the filter or the pipe for that cost. Maybe the coupler and clamps.

I was quoted $70 for a K&N REPLACEMENT filter for our cars.

You can get a K&N cone filter from ajusa.com for about $50.