well if you got an exhaust i suggest an Intake
(i know GTS models respond well with Intake
and exhaust). for cosmetics maybe tint your windows, get mtecs,...on the cheaper side...maybe a body kit if you have the money. handling-springs,shocks,sway bars...cheapest suspension mod is a front tower brace that they sell here...the rear tower brace is good too by hypermotive or TRD
...ummm i dunno, what are you trying to go for exactly?