First of all, this is not the proper section.
Second, I have a feeling that you do not know anything about building PC's?
Because with only one GTX 580 you already have 4000+ MB of Video Memory; so you won't need a 2-way sli.
I'd go for a Twin-Frozr II by MSI, I have it and it runs BF3 whilst recording with Fraps AND livestreaming at a steady 60 FPS.
Also, that graphics card runs 3D graphics as well, if you'd like that.
Third, Why the hell are you trying to buy a Crossfire account for that much money? Could aswell buy a better game or invest into one yourself ...