I just bought a used revelation mini for about $70. eBay is your friend - can't build one cheaper.
If you're somewhere bereft of ebay and commercial stuff has crazy markups, you're basically looking at a blow dryer attached to a sous vide PID controller and some sort of constant stirring device. Not easy to fabricate, but not impossible.
I'd just practice using the microwave. An electric blanket will help you evenly warm it if it gets too cool.