What's it worth?

2006 Chevy HD 2500 crew cab. Duramax diesel Just under 100k miles. XM, 6 disc CD, heated/power seats, rear seat DVD system, Heavy duty towing (But no electric brakes installed), line-x ed bed and running boards, color matched fiberglass topper, new street tires on aluminum factory 8 lug rims. The transmission is the Allison 6 speed with the tow haul mode, It has the Bose sound system and the seats are leather. Owner just had the injectors cleaned, radiator flushed, a new transmission line put on, brakes checked (Still original, and not recommended to be changed).

I need to get a larger pickup and would like the diesel. Don't want or need a 1 ton or dually, so this seems to fit the bill.

What do you guys think it's worth and what I should pay for it?