No worries at all using aftermarket steel rims. When I had my Grand Prix I bought aftermarket steel rims from Harland Pontiac Buick in Dorval for $50 each. Costco sells them too. The bolt pattern is 5 X 115mm, though 5 X 114.3 is more popular and more widely available. I think even Mercedes uses 5 X 114.3.
There'* some debate as to whether you could safely use 114.3 on Gm vehicles but I've yet to here of a problem.