Powder coat w/ a clear powder coat over base = glossy and super durable, but not cheap. If you do the prep: strip old finish off, degrease, and possibly sand-blast yourself, you should get a better price. As for the cost, it depends on how competitive shops are in your area.

Black is a common powder coat color, so you may get lucky and find a shop that will run your wheels thru along with another work order that's being powder coated in black, and they may cut you a deal since they won't have to switch over to a new color just for you. Also, ask them what kind of 'hangers' they need to use when they spray your wheels, and you may be able to make some for them to use if they don't have any. . .