I got inspired by the Propagation Dome post started by BoyerHoldingsLLC to post this. Here's my no cost propagation dome:
(Sorry for the quality of the photo)
2 bins, 1 light bulb, 1 light socket = Budget Propagation Bin.
I had the bins and the light bulb already. I salvaged the light socket from a lamp that was on it's way to Goodwill. I drilled a hole in the bottom of one bin with a hole saw, threaded the lamp socket through it. It helps to have the kind of light socket with the screw thing on it so that when you screw it together the outside of the hardware holds the light in place. For a second bin I made I had to McIver the part to hold the lamp in place. This is your "top."
The bulb provides heat and light. Although I haven't found mine yet, you could use a heating mat under the bin to provide bottom heat. I drilled four holes at the four corners of the top bin to vent some of the heat. You can even put a few plants or seedling trays on the top of the top bin to provide bottom heat for those plants (hope that makes sense). It will accommodate 40 (5 rows x 8 rows) 3" containers.
That's my homemade doohickey. Anybody want to fess up to theirs?