My truck cost $35,000 out the door in 2003. Ordered the truck at local Ford dealer for $200 over invoice. It was drop shipped by the factory to Rayside Truck and Trailer in West Palm Beach where they mounted the bed and installed the RevPak behind the cab. They painted the bed and RevPak to match the cab. The total price included the Rayside work.
The truck is a base F450 crewcab XLT. (V-10, 6-spd, 4.88axle) The only options were trailer tow package, running boards, and carpet delete. The rebate covered a little more than the sales tax.
At
http://donandcharlotte.com go to page 2 of the albums to F450 Camper Hauler to see the truck.
Above post is correct. It isn't a simple matter to drop a bed on a cab and chassis. When you center the wheels and wheel well there is a 4" gap between the bed and the cab. Also, the frame is about 7" too long behind the wheels. You have to whack off behind the last cross-member. There is other stuff, too.
Rayside only had one F350 dually bed in their lot when I was there. So they used it for my truck. They had a big stack of F250 beds however and dually fenders could be used on them just as well but it would add to the cost. They get the beds from people who convert to utility bodies and flat beds.