Low buck stuff would be:
Cold air intake, header, 2.25" exhaust, sr20 throttlebody, underdrive crank pulley, advancing the timing and running premium fuel (free

), ditching the A/C (sheds a ton of weight), maybe look into weather or not there is a manual rack and pinion to get rid of the power steering pump, redline MTL in the tranny. Thats what i can think of at the moment.
Pretty much everything after that increases in cost exponentially. ie, engine rebuild with custom pistons, lots of machine work, cams, port and polish the head...alot, lighten rotating mass (flywheel, butchercrank, aftermarket rods) the list could go on for pages.
With the low buck stuff, you could possibly see a net power gain in the neighborhood of 10 maybe 15hp and an equal amount of torque.
In anycase, in general, the basic rules for tuning is the same for all engines: an engine is an air pump, the more efficiant it is at moving air in and pushing it out, the more work it will do (hp and torque).
And remember the addage "speed=money, how fast you wanna go?"
Cheers