What should I charge?

[Espeefan]

Why not encourage him to build it himself? Maybe instead of you doing all the work, you could offer to assist him, if he is local to your area, and when he gets hung up. Unless he wants a custom truck, there shouldn't be any reason why someone couldn't build a box stock Tamiya. The manuals are some of the best in the business. Maybe you'll make a good friend in the process.