I had the tower in my profile pic powder coated for $150. He did say that if I wanted another one done it would probably be between 200-250. But the tower we made on our boat is huge as well.
I'd have thought it'd be better to ebay/craig list your current monster tower and just buy a new one. They offer Black and it'd probably cost the same in the long run.
Powdercoating a tower should run between $175 and $250 for a walk in customer. If you add a gloss overcoat the price may be more. If the powdercoater is looking for work, he may give you a better price.