Depends on how much you really know about engines and if you're going to be doing it yourself. You could start with simple bolt-ons like a cold air intake, headers and exhaust and then work your way to ported intake manifolds and ported cylinder heads.
For $1500 you could do the intake, exhaust and headers. If you know your way around an engine, a performance package is also an option:
http://wot-tech.com/shop/performance...s/cat_106.html