Which parts did you have in mind?
I'd really recommend a i3 2120 instead of a fx 6100.
I'll redo the build with the i3 2120 and show you the pricing again.
EDIT: Here's the build.http://pcpartpicker.com/p/6hHl
If you want to keep all the possibilities for SLI/CF, you can keep that ASRock Extreme3 Gen3 Mobo.
Here's the build with a 7850. (Still under $900)http://pcpartpicker.com/p/6hHF