i painted my first set of alloys not so long ago for a mate that couldnt sell a car - it was a rush job but they came out quite well, not a pro job but the car sold a few days later!

rubbed them down with emery, etch primer and then alloy wheel siver. didnt cost much at all (cant remember how much)

no idea if they still look good now but i did key them up really well and as said, heat the alloy before applying the primer