Unfortunately for the Focus no one makes a true coil-over kit for the rear yet.

Ground Control does have a nice setup but the kit rings in in the low $400s. Koni is the only manufacture so far to have shocks/struts for the Focus and they cost about $550 on the average for a set. So for that price I can get the H&R kit which has dampers specifically valved for the springs for only $150-200 more. Plus H&R has a lifetime warranty and I can probably sell them to someone else if a better suspension kit comes along somewhere down the road.