Ehh, if your charging system is already not doing so hot I'd stay away from the UD pulleys. You can find a good CAI that is used for ~$80-$100, a 160* t-stat for about $25, a manual fan switch for $40, a blaster coil for cheap, MSD plug wires to replace your old ones for $80, a short shifter (if a manual) for $150, Drag Radials for $300 new, prolly a new torque arm you'll need for about $250, airfoil for $30, intake elbow for ~$75-$125 depending on brand. These are all relatively inexpensive and would go well with headers/exhaust.
Now once you get past that point you start looking into and Electric waterpump, 1.6 roller rockers, and maybe even a mail in tune. These are still fairly cheap, but take a bit more work (minus the tune.) To get the gains.
After that you're pretty much headed into heads/cam/spray territory unless you get all of the suspension outta the way. Hope that helps.