ChemistJason, the main cost is the chassis as it is a one piece unit. Everything is more robust as they are built mainly for long term (miles) passenger buses.
The other costs related to the conversion is that everything is custom made, it's not on a assembly line.
When the chassis is driven to the converter, it is an empty shell inside with a small temporary driver's seat. The slides are put in at the factory in Canada before it's sent to the converter. All the conversion is done after the shell is built. I would imagine that the front windshield is removed to put the appliances in along with any other large items.
Our converter paints the exterior before the inside is even touched. The whole painted surface is covered with a styrofoam material for protection and then the conversion starts and takes about 7 months.
Another cost are the amenities. The total cost will depend on what the customer wants inside.
Mark