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Check the auctions here, check your local Craig's List and feed stores. See what's offered, research it to see if it's what you want.
With that price limit, you are unlikely to get one that has any frills. Do a search of BYC for "homemade incubators". That will save a LOT of money.
I'm not going to do all the research for you, there are already many threads about incubators that will help you. I would also like to suggest you read a lot in the Hatching topics, so you know HOW to incubate, too.