Intake is the best performance upgrade, but for $350 your options are limited. You can also do some mods that won't necessarily give a high power boost, but better your cars current performance ie. Johnson pump $135, LET Phenolic Spacers $80, and some K&N filters I think they are $42 each (find the thread on stock intakes choke point and remedy that or ask LET since they found it). Your car should be pretty decent after that.