Check with your local high schools and colleges, I got mine from a college for a VERY discounted price(free). It's also a hot plate which can come in handy as well! Often they'll get rid of things for senseless reasons, for mine, the cord was burned through. They were just planning on tossing it, $5 and a new cord later, its good as new.
There's also some great DIY how to's out there. Stir plates are reallllly basic things, it's literally just a spinning magnet and a table. I've actually thought about integrating several stir plates into my workbench.