I've been buying the emu/ostrich incubators, gqf model 1527 and 1536 from various craigslist sellers for $150 or so each. They're so cheap because no one is hatching emus or ostriches, and people don't know that they work great for other eggs, too. The trays are horizontal rotation, vs the other tray style by gqf, the vertical rotation.
All you have to do to make this tray work for other types of eggs is cut a piece of hardware cloth that is a little wider than the top of the tray, bend it into a C shape, load your eggs and then secure it with zip ties, as shown in the picture. Click on the picture for a bigger version. When the eggs are done with the rotation period, you cut off one side and remove those eggs. So for $5 worth of hardware cloth (the metal mesh covering the eggs) you've got a $1,000 incubator! ($639 for the box, plus $119 for 3 trays...)
Each of these horizontal incubator trays will hold 75 large chicken eggs or 60 turkey eggs, and there are up to three trays per incubator, for a total capacity of 225 chicken eggs or 180 turkey.
If you buy a used GQF incubator, what you need to check is that the unit will make and hold temperature -- you'll want it to be at 100.5 or so most of the time. Have the seller plug it in and have it warm up for a couple of hours before you look at it. Check that the tray rotation mechanism isn't frozen. If it is frozen you can usually take off the rear cover of the hatcher and tap the lever with a hammer to free it up, but sometimes the mechanism is so crudded up that it either burns out the motor or is glued permanently. If that happens the replacement parts will be relatively expensive, so don't pay more than $300 for a used GQF incubator or you'll run the risk of the repairs costing you more than just buying a new unit.
The emu/ostrich/goose models (1527 & 1536 have little plastic gears that break if they're manhandled, so be careful pushing the tray back into the incubator. The temptation is to grab the tray and use your hand to align it by moving it up and down, but do that gently so you don't break the plastic gears in the tray. If you do, you can buy them from GQF for $5 each, but it takes a careful 30 minutes to take one of these trays apart, replace the gear, and then put it back together.
It is worth it to buy the humidity bucket setup sold by GQF if you are going to use your hatcher a lot. Instead of having to open the hatcher every day you pour 5 gallons of water into a bucket every other week and you're good to go. Makes hatching pretty painless.
I have no connection with Double R Supply other than as a satisfied customer.