That's a pretty good number, but that's A LOT OF TRUCK! It's like detailing a Tractor/trailer.
You could spend 2 days just on the interior....
You probably should check the condition of the vehicle before giving a quote.
Tar, carpet mud, stains, paint condition, etc.
Does he want it waxed/polished? Charge more.
I always do an estimate based on $35 an hour. Multiplied by 20 hours work would be $700. If you're willing to take less, you might get down to $500.