Build Your Own Hackintosh Mini

"We've shown you how to build a Hackintosh with enough power to rival a Mac Pro, but for those of you who want a still powerful Mac on a budget you can build a Hack Mini. We'll show you what you need to build it and walk you through the entire OS X installation."

And walk through is the key here, as they really detail it step by step. Nice tutorial that, without accounting for your time, will cost you less than what you would pay in the Apple store. Of course it won't be quite as small as the official Mac Mini but it is pretty small.