well you can get a g-max kit for about 210 pounds (plus packing) which will drop it 40mm and is a good quality kit if you have sensible mods,eg chip,cam actuator,but if you intend to go for more power in the future then id spend a bit more and go for koni set up which you should be able to get for around 280-350 new or used!
try someone like burton power products in ilford in essex england,or there is woodford motorsport,jondell motorsport..........
not only that but they say they will probably outlive your car