The large floorspace is because of the temperature gradient needed... from 120+ basking surface temperature, 95-100 ambient air temp in the hot side, and 80-85 ambient air temp at the cool side. It's really hard to get the correct temps in anything smaller than 36" x 18", and even that's sometimes difficult.
Right now I have two baby Saharans in an enclosure that size (36" x 18" ) and I have good temps, but I also work from home and I'm constantly checking temps throughout the day and covering/uncovering part of the screen top with foil to keep the temps correct. It's do-able, but you'll REALLY have to watch the temps. We're upgrading to 5' x 2' enclosures this spring, which will be so nice and much easier to maintain good temps.
Hope this helps out...
Andi