If you're buying a second hand machine as a backup, presuming that it's in sound condition, you should not pay much for it. You're not in a hurry, so only buy it if it's a bargain. As Mark says, consumables are standard on most machines. A Minuteman distributor here in the West Midlands is Scrubtec on 0121 240 6624. Their 2002 pricelist shows the Rugmaster 7 at £1100 and the Rugmaster 13 at £1180. The "7" and "13" relate to US gallons capacity. Hoses, tools and V.A.T. extra. Both are single 3 stage vacs and 100psi pumps. These are the only conventional extractors listed, but there are other spotters and walk behinds.
Safe and happy cleaning:)
Ken