It's not too bad. The link you posted is for coil-overs. Those are adjustable, and people like them because they can lower their cars with the spanner wrenches. If you car is just a daily driver, you can buy plain old stock aftermarket shocks. Also, I think you said the front is already done, so you don't need those struts that come with the kit. I don't know where in the UK is the best source of parts, but shocks are very affordable, even good ones.
Toby