Any good auto shop that has technicians ASE-certified for steering/suspension work should lower the car for you.
The lowering kit will include replacement coil springs, and probably new shocks or replacement shock bolts (a camber kit) to make camber adjustable. Since lowering the car will change its suspension geometry, you may also need several replacement suspension components (such as spindles or A-arms), also to make it alignable again.
Lowering a car properly is straightforward, but tends to be expensive depending on the quality of work you have done. The Cobalt is a nice car; please have the best quality work you can afford.
Be forewarned: don't cut or heat-treat your suspension springs or bend any suspension components to lower the car! The suspension springs will be unable to hold the weight of the car, and bending the other components will permanently weaken them.