What is the value of my truck?

I have a 1989 ford f-250 4wd, dual tanks, 460 engine, power windows, power locks, cruize control, manual locking hubs, and a manual 5 speed transmission. It is overall in good shape exept for a rust spot in one of the panels of the bed, also it is a regular cab with long bed. I have put clearence lights on the top, and a diamond plated toolbox in the bed. Can anyone give me an estimate of how mutch this trucks is worth, or a bluebook value, as I cant find a straight answer.