If you want the prep-work done right, do it yourself. Painting a one-piece wheel is no easy task if you want it done as clean as possible. Starting off with a powdercoated center will make everything easier. Trying to prep the chrome for paint isn't easy, nor was it recommended by any of the shops I visited. Take that for what it's worth though, because there are many people out there with colormatched wheels that began as chrome wheels without any issues.
Feel free to check out my colormatching thread:
Color-Matching KMC Dimes