My guess would be 2 or 3 hundred for a good paint job. To be sure, I would recommend asking a shop that you trust for an estimate. If you did have it painted, the outside would be as good as a new one. The Snugtop is a high quality shell and I would recommend a quality paint job to match it.
By the way, I'm not selling the shell because I'm dissatisfied with it. I'm planning on installing a small slide-in camper on my truck. I set the price aggressively since I don't have much free time to handle the sale and I want to get the slide-in as soon as possible. I shopped around and feel the Snugtop is the best of it's type for the Titan. I am very happy with it's quality and look on the Titan.