My truck has a private party sale price estimate of about $11,000. I expect the same truck with a gas engine would sell for several thousand less, but maybe not as cheap as you are looking for.
The truck has about 140,000 miles on it. The Allison transmission is a 6 speed automatic. They are generally regarded as very dependable. I think the upgrade when new was about $7,000 for the transmission.
I get about 16 to 18 mpg empty on the highway, still about 10 mpg hauling a 5,000 pound gooseneck trailer and 12,000 pounds of logs.
I had a 1986 Chevy 2500 pickup before with a 454 engine. It really sucked down the gas. It got 9 mpg empty and 6-7 mpg with a load. It ran OK, but was only 2WD, getting too old and cost too much to drive in 2008 when I got my newer truck.
I figure my 2005 Chevy truck cost about 35 cents per mile to drive empty.
I am replacing the brake lines on it today and that is the most significant repair I've had on it since I got it in 2008. Total cost for this repair is $120 for parts (all new brake lines) and the local shop said they would do it for $300 to $400 labor. I'm doing the work myself since I'm too cheap to pay someone else for something I can do myself. Their estimate was 4-5 hours labor. I'm about half done before the rain stopped me today and expect it to take me about 6 hours total.
The only other non maintenance repair has been replacing the left front hub.