www.lmctruck.com is one of the better sites to go through for classic truck parts, including new body panels, trim pieces, emblems, flooring/carpets, etc. There are probably a hundred or so more through eBay, too. Some with new and some that are parting out...check their reputations first before buying.
By chance I just stopped at the local Earl Scheib and they quoted me between $350 for a quickie-no-frills basic shoot with one of their standard colors and $1500 for a good job done with UV protection, topcoats, and warranty. Too rich for my blood and was equal to the value of my own truck!
But if you can find the orignal color paint, small areas should be easy to fix since that year didn't have any clearcoat. Just a matter of sanding down to bare metal, detack, prime, sand, paint, buff, & polish. Fixing rust holes and dents is more challenging since you have to learn to use Bondo and alot more sanding involved. The right tools make this alot easier.
Finally, couldn't find info for your '83, but an '85 C10 with the 5.0L and 4-speed automatic was around 13-14 mpg city, 17-18 mpg highway...not bad.
Good luck & have fun with that truck!