If you have multiple snapped springs it will definitely be cheaper to get some after market springs. The front springs themselves are £110 each plus labour to fit. I think Eibach Pro-line are £190ish for four or H&R about £150. You'll be looking at at least £300 all in I would think.
I went for H & R in the end, the shiny new parts should be with me on Tuesday, found a garage that will replace the snapped parts for £140. Should get my car back on the road for about £450 all (including some part worn for the front)