Well computer cases aren't
too expensive. Sure, they may not be the best quality if they're cheap, but at least it'll work.
I saw a computer case that would be around $80, a power supply for about $50, the graphics card I had my eyes on for around $150, yet I hadn't really picked out a processor just yet.
And let me just say, the thing that sucks about all of this? The computer I currently own is $2000 from when I bought it back in '09. I know it would be less now, but even at that price and with the specs it has, I can guarantee I was ripped off. ;-;