Early this spring I bought a GQF Sportsman cabinet model from a friend for $150., and thought I got a great deal. For some reason I kept checking Craig's List every day for incubators and REALLY lucked out.... I found two more GQF's, one a Sportsman incubator the other a GQF hatcher, in great condition for $50. each. I grabbed them up so fast my own head spun!
So, check Craig's List every day, maybe put out a wanted ad on CL. If you're looking for a smaller unit, maybe a wanted ad on Freecycle. Great deals are out there if you're patient and persistent! Good luck... but be forewarned... hatching is addictive!