I believe the max overall is 45'(though I think I have seen 47' bus conversion recently). I know states like California max out at 45', others may be a little longer.
A a full blown truck conversion on a new twin screw chassis w/ multiple slides should still come in under $200,000.
If you get something going be sure to keep us updated.
2003 28' Show Hauler Motorhome on a 1995 FL 120 completely refurbished chassis.
Currently in production - scheduled completion 1/10/03 www.showhauler.com