I guess I'll chime in as I run a run a resto paint and body shop. It is absolutely impossible to come up with an accurate figure, but i will give it a go and offer some advice on price options.
1. It all depends on the level of quality you want, and the existing condition of the truck. If it is rust free and is just in the average shape of a normal work truck, then I would say that around 3K is a fairly good estimate if using quality materials. If it needs minor rust taken care of and it's a little rougher around the edges than 5K is more along the lines of a resonable estimate.
2. If you are just looking for a 10 footer using mediocre materials (synthetic enamel or low end bc/cc such as Kirker, then I would say 1800-2500 is probably about right. This would be a finish that looks decent and hold's up well, but is definitely not a show truck.
3. Or... you could take it to a place like Maaco
Now I know that people will tell you that if you do your own prep work, then you can take it to maaco and get a decent job done, but it just isn't true. Sure they can spray the paint, but any trained monkey can spray paint. A good finish is 99% prep work. Also, budget refinish places like Maaco and Earl Schieb use acrylic enamel that they buy in 55 gallon drums. This is why they can spray a car for $250.00 whereas I can't even buy low end BC/CC materials to paint a truck for under $350.00. Acrylic enamel is the same paint you can buy at your local tractor supply, it's farm implement paint (and that is the only place it should be used with today's technology). Now if you want to pay for the higher level finishes than Maaco can do a good job, but for the price you would be better off just taking it to a reputable shop and getting a good warranty and peace of mind.
If you have any questions about the process or materials just let me know. And if you are serious about getting it resprayed, I would always give a heck of a discount to a fellow oilburner!