At least you've got a realistic budget! Too many muppets expect to get motorsport pedigree coilovers for 2-300 quid!

I've got Koni's in my Focus which have always served me well but you need to regularly adjust both the height and the damping to stop them seizing. Have you looked at Bilstein's as well?

If it was me. With that budget, I'd go for either the Eibach's, Koni's or a set of Bilstein's. All 3 company's are heavy in motorsport know-how so you can guarantee you'll be getting some good bits of kit.