Only thing with the focus is that the wheel offset is between ET42 and ET45, which means that escos wheels, and even normal escort/mondeo etc alloys won't fit without scrubbing the arches as they will only be ET38 at the most. I tried a set of alloys on my old focus that were ET38, and they scrubbed the rear arch.

ST170 wheels are expensive, I sold mine for £450, but keep looking out and you will pck up a bargain with a scruffy set that need a bit of paint