Try not to use a APU :D
http://pcpartpicker.com/p/1I4yx
That's what I came up with... You could go with a cheaper motherboard if you're really short on money, but that's my best bet. If anyone has any other system build, be my guest to post.
edit: you could also cut down the case price (and maybe you'll find one that looks better to you for cheaper who knows) edit 2: Maybe this psu also, if you can get the deal. Rebates are a pain because you still have to have the money on day one.
http://pcpartpicker.com/p/1I7zT
Wait for the new GPUs, the low end gets like an extra GB of ram.
Best i could do http://pcpartpicker.com/p/1I7XI
If you cant go over 450 you should get the 7850 instead of the 7870, in this build anyway
If i were you i'd wait for amds new gpus announced yestersday they will be better value for money