Without seeing the vehicle, it's almost imposible to give an exact estimate.
This being said, for a basic wash, exterior only (I'm guessing there's no sleaper), I get around $95; for a wash and wax, double that. If I have to turn on a buffer (polishing) no less than 3.5 times the wash price. Wheel polishing, no less than $60 per wheel.
If the truck has polished saddle tanks (most do), and the owner wants the entire vehicle washed, polished, waxed, as well as the wheels polished (basicilly a complete exterior detail) I might offer the owner a discount if he does everything -- say the whole thing for somewhere around $750 or I might approach it by offering the interior as a "freebie for around $800.
As a foot note, it's been my experience that unless it's a show truck, or being sold, or just purchased, that these types of jobs are hard sells to the average trucker.
Good Luck, and expect to spend the whole day (8+hrs) with at least one helper if they go for the complete detail.