Wheels and tires can totally remake the look of your car. I would start there. A good set of 18" wheels with performance tires will set you back about $1300.
If you go that route, the link below is a place I have bought two sets of wheels from. They are reasonable, ship fast and know their stuff. Also, their site has a cool wheel viewer so you can see different wheel brands and sizes on your Celi. Discount Tires and Wheels
After that I would think wing/spoiler if you do not have one and a set of TYC Elegante tail lights (about $200 for the lights).