While many polish themselves, I farmed out my polishing work. I paid $80 to have my fork tubes polished professionally as an example of pricing. While it may sound like a lot, if you're not already set up for polishing work, you'll spend a bit of money on equipment/materials anyhow. So if you're going to do a lot, and enjoy doing it, get set up. However, if you're like me and don't have the setup, the workshop or the inclination to do it yourself, there are folks out there who will do it.
Powdercoating is cheaper, but not by a huge margin. Coating two fork tubes would likely run $50 or so, maybe more.