As others have said, something that size just isn't made to haul. The difference in gas mileage savings will get eaten up in repairs.
You can find a decent hauling vehicle in that price range but it will take some looking and waiting for the right one. I bought a new (old) truck last year - it's older but it's in great shape. '91 Ford 3/4 ton with a 460 in it - not a speck of body rust and the best part is it only has 40k miles on it. Runs like a champ and price was under 5k. Gets better mileage than the diesel - get about 17-18 when it's not pulling, about 14 when I'm hauling.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.