I owned a st170 a few yrs ago. .till it got written orff by a rogue 4x4 ! Only problem I had was the dual runner cable snapped and the p/steer pump went.. Being of the Focus RS origins is totally different to a daily focus p/s pump. Local price was $1200(!!!) So I bought a new one from USA at $85 plus $40 shipping.
A lot of components are different to stock focus, like massive brakes(300mm) , gearbox is 6sp , suspension, interior. Very unique car as we only had 125 of them here in Aus making them ultra rare. .
Sorry for the carry on but I reckon buy her a mk6 fiesta(06-09) as only a few Grand now and plenty reliable , cheap to run etc.