I recently had this done in New Orleans. I had them sand blast off the old paint, parkerize it, then powder coat and it was $300 sans tax, owing to cash payment. I could have haggled the guy -- the shop was empty -- but he was honest and skillful. It would have been another $75 if I got a custom color, but he had what I wanted left over from a previous job. Add more if you want them to plug tapped holes, or do much complicated masking etc.

Parkerizing/pickling/phosphate conversion coating/bluing is dipping steel in a chemical bath which builds up a resilient and corrosion proof layer. Firearms with a blue/black appearance are typically an example. 100% worth it on a steel frame, I believe.

Travis