There are a number of places that will widen wheels. Either steel or aluminum. See:
http://www.weldcraftwheels.com/ as an example.
I just bought a pair of c5 z06 rear wheels that were widened to 12" from the original 10.5". The wheels are GM forged aluminum manufactured by Alcoa that came on 2001 z06's.
Widening generally will add offset to wheel (they add on to back of wheel). You have to make sure that you have enough space in the wheel well to run the wider tires. My car has been mini-tubbed so I have space for the wider wheels and tires.
Probably will be tough for you to do on a budget. Think widening will be at least $200 a wheel. You would have to start out with a 19" wheel that fits your car, the wider the better. Maybe a pair of used 19x12's off of a c6 z06 or a aftermarket set. The project is going to set you back more than $1000.