HI-Spec don't do anything for a Focus. But they do have a 6 pot conversion for an ST170.

I'd go for a basic ST170 conversion. All you need are the discs, calipers and hubs. I bought mine a while back for £150, since which I have upgraded to AP Racing 4 pots...which I still need to fit!

But that's your best bet, 300mm brakes for near no money!