I would start at the low retail pricing of $39k. I would deduct 20%, or about $8k. Then I would deduct for new tires, ceiling repair, batteries, belts, mechanics bill, so in the end you would be at about $18K to $22k offer.
I would have a real diesel mechanic work with you on the initial start up. Lots of filters and fluids to change before you ever crank. But, it will probably start right up unless there is unknown engine damage. You didn't say how many miles, over 100k miles and I would drop the price another $5k. Just my opinion.