I was looking around for an inexpensive stir plate when I found a few examples of making your own. So with a few extra computer parts, I was well on my way. The only purchases that I had to make were the potentiometer (to be able to fine tune the speed) & stir rod. Together, less than $5.
I made use of an external hard drive that no longer functioned and a spare computer fan. I used the hard drive as the base/body of the stir plate. After gutting the hard drive I disassembled the drive to get the powerful magnet. Installed the computer fan, centered & glued the magnet and wired everything...
I made use of the original 12v power supply on the hard drive and wired from the supply, to the existing power switch, to the fan, then to the potentiometer & back to the supply. Sealed everything back up & drilled a spot for the potentiometer on the faceplate.
Now I have a fully functional stir plate for less than $5. It obviously depends on what spare parts you have around the house, but if you search for more examples of home made stir plates, you will see a majority of the people using cigar boxes or old Tupperware containers and only having to purchase a computer fan & potentiometer.