Be weary of good body shop rates. I've yet to find a single body man that I could trust.
I'm tripping over 87 and up beds that are practically mint (******* me off, because I need one for 86). Saw a CL ad recently for one that was used as a show room piece for a canopy outfit and never saw any rain, direct sunlight or salt. Rhino liner and all.... Saw another dual tank 8' bed in the auto wreckers yesterday that was an absolute cherry.
What you have to remember with having dents repaired is no matter how good a job he does, most body men prefer to just heap on the bondo. Also, when all those dents are pulled out, the factory primer cracks in places like the inner wheel arch and you could have rust oozing out of there in a couple short years (assuming it hasn't started already. My understanding is these truck bodies are immersion primed at the factory so all the inner seam and lap joints have primer in there, but when you stretch the metal enough, the protective layer gets breached (usually near a spot weld). Places like the wheel arches and rear box corners are VERY vulnerable to rust even at the best of times, let alone when you go stretching an bashing the tin like that. The only real way to stop the rust is to oil up the body periodically (A good idea anyway), but considering you will likely pay the same amount for a whole bed, I would just replace the whole thing and not worry about what your fresh paint could be hiding from you.
I say look for a clean bed, have it painted, THEN drop it on your truck (unless you want to do the whole truck over again, which it seems is not needed).