Price on the used incubators varies greatly depending on location, around me for a still air you are looking at 40.00
I would get forced air though.
I have been running into many around me that have ditched LG's for Hova's and ditched Hova's for LG's, it seems they believe they just put eggs in and out pop chicks.
I now have 8 LG's, most were bought used with the common comment "it won't hold temp", well, I bought digital thermometers and have run each for days with fluxuation of 1-2 degrees now. I have had the opportunity to buy some Hova's but passed as they were still air.
People also forget that when you add water the temp will drop unless you are adding water that is the exact same temp as the incubator, and when you first add the eggs the temp will drop.
What I have learned, whatever brand you get, use forced air, use digital thermometer, calibrate the thermometer, don't adjust temp every 15 minutes (if it stays at wrong temp for several hours then adjust), normal fluxuations are ok
FYI: I had the same hatch rate in my LG's with my call duck eggs as the person using a GQF sportsman did.