£451??!!
They are the easiest springs in the world to replace, if a garage charges more than an hours labour then they are ripping you off (will be done in less than an hour).
Even the rear struts are quick and simple to swap.
See how much the springs are from TPS, or a dealer if your local won't sell to you, then have a garage fit them if you don't want to do it yourself. Will be nowhere near £451 that way