Where can I get the cheapest gaming computer tower?

Where can I find a really cheap computer tower that is great for the sims 3? I have a screen monitor all I need is a cheap computer tower. I play the sims 3 so maybe I don't need a really extravagant computer tower. A website that I can order one would be great and a suggestion on what type of computer tower I should get (not best buy or staples) the sims 3 (from an estimated combination of the base and 3) packs needs at least 15 GB** (about 3.5 GB from each one) of free hard drive space. In case that helped anything