What plans did you use for the DIY incubator?
The plans in my head as I went along

I just winged one day it with stuff I mostly hand on hand as a proof of concept, and it worked so well I use it as my primary incubator... The only initial purchase I made was a water heater thermostat about $10... And when I built the egg turner I purchased a motor for that, pretty much everything else I had laying around...
The incubator is built in a foam cooler, the particular one I used was used to deliver steaks in the mail... I made a heating chamber out of some scrap heating duct, a used computer fan, a porcelain light socket and a 60W bulb that was all laying around... The viewing window was an acrylic shadow box frame, that I got at a resale shop for $0.99 cents...
The egg turner I made from mostly scrap wood and a few dollars worth of wood dowels and the give or take $15 turner motor... I fabricated the aluminum control arms myself from melted aluminum cans... I can adjust the turner for different egg sizes by simply moving the dowels or building a new tray...
Even if I had to purchase all the stuff, if I shopped around and was frugal I could build another for cheap...
Some random pictures in random order, be aware I use this mostly for chicken, guinea and peafowl eggs but there is no reason it won't work for quail with the appropriate sized tray...