I've used the rattle cans mixed from a paint supply shop. They are $18 a can here locally. The blue and red that I have used played down really thin and clear. It took ALOT of coats. I sprayed the clear on pretty thick. After a wetsand and buff it looked GREAT.
But I think that if you just want gloss black and it doesn't need to be a perfect match to any other existing paint. A vinyl wrap could be very cheap, easy, and DIY.