You can use a ceiling fan motor and a plastic bucket to make a pretty decent pottery wheel for under $50. The most expensive part is the ceiling fan, and you can pick those up, on sale, for $30, or at a garage sale for even less.
History: My kids were both into pottery, and really wanted a wheel. Decent wheels are pretty expensive, but luckily a friend of mine had a Clay Boss pottery wheel, and loaned it to us for a few weeks. We had a lot of fun with it, but alas, had to give it back. I recently picked up an old ceiling fan that one of my neighbors was throwing away, and I realized I could use the motor to make a pottery wheel, similar to the Clay Boss. Here is a link to my original inspiration:
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I Could Make That Contest