This is an incubator I built to hatch out Ball Python eggs. It worked very well for me. It was about $150.00 in materials but if you had a cooler laying around, it would be cheaper.
I believe it would work well for other reptile eggs but you will need to read up on the requirements.
This incubator goes together quite quickly and will be able to hold three 10.5 x 7.5 x 4 inch "shoe boxes" per level. You can have two levels in a cooler of this size. It takes about 30 minutes total to assemble once you have all the supplies on hand. It also took about 15 minutes after it was complete to come up to temp and hold it. When you add the Egg boxes with media inside, it will take several hours to rise the media to the proper temperature so allow, at least 24 hours for all to come together prior to needing it!
I am not an electrician and I post this information for reference purposes only. This is simply what works for me. If you have any suggestions for improvements, please feel free to share.
Step 1: Materials
70 Qt Coleman (or similar brand) Xtreme Cooler
Flex Watt Heat Tape 11" Wide Tape (110V) (20 Watts per foot)
Flex Watt Cord With Attached Copper Clip Set
2" Wide Professional Foil Tape (UL Listed)
BAH-1000 Thermostat (1000 Watt Triple Plug-In)
Themometer with Probe
2 Racks (I used raised cookie racks for the bottom rack and a piece of closet rack for the top)
6 Plastic Egg Boxes (Tupperware is great!) around 10 x 8 x 4
Hatch Rite (egg container media)
Various self-tapping screws