Sounds a little steep to me, but there is a lot of value in a low mileage 7.3. Big thing would be to get the motor checked out to make sure it is in good working order and then you really know what you've got. Things like house water are pretty inexpensive to deal with if you've got a rig that has a solid drivetrain, especially a 7.3 with 4x4.
2015 Chevy Express 3500 Duramax
w/ Quigley 4x4 & Agile Fox shocks
Sold 2005 E350 Chateau
Quigley with Agile RIP, 6.0 PSD