In the market for a Cobalt, some questions though

Im new to the whole sports car market and everything associated, now that we've established that lets continue :p. Basically I have about 15,000 in savings right now but im not sure what I want to do. After my friend taught me how to drive stick, I see no other alternatives the amount of control and performance you gain over an automatic car is staggering. And ever since he took me out on his upgraded talon and let me drive that around ive been addicted to fast cars. And im certain that the cobalt is the car for me im just not sure which build. Basically im not sure which builds allow for specefic improvement. Ideally I would want to buy a SS, but I dont think that will be the case, I know the cobalt is only a 4 cylinder car but its light weight makes up for that I hope even though I havnt actually driven one yet. Can you upgrade the LS/LT's to SS stage 1's, and then progress to 2 from there or how does it work?

Thanks