wowser, £45 sounds more like it. I just had my n/s/f spring replaced, the garage phoned around ecp, partco etc and they couldnt provide it. phoned renault direct they charged him £115, for one spring. he nearly choked, as did I. (think it cost £65 for both on my old golf gti when i replaced them a few years back).
only difference I can see from the OP's description is mines a non-cup 182 sport (54 plate)...which I would assume would be a different spring, but not make it £70 cheaper????!!!
fortunately i had it covered under warranty so only had to pay a £25 excess. which is nice. not looking forward to when its out of warranty.