Someone should sticky this.
I disagree about the earlier statement about cams. From what I've gathered, the cams in the 7M are robust enough, in both the NA and the Turbo motors, to support high HP.
Besides maintenance issues, this is where I would search for "inexpensive" HP in an NA:
1) Intake
2) Exhaust
3) Header
4) Ignition
5) Fuel
6) Electric Fan
7) Flywheel
8) Underdrive Pulleys
9) Ceramic Coatings
* 50-80 Shot Dry Nitrous setup
This is for going all out:
1) Headwork
2) Cylinder Overbore
3) Rod/Piston Upgrade & Compression Bump
4) Tuning
* 90+ Shot Wet Nitrous setup