Hi Andy,
Having just gone through the whole kitchen thing I feel for you!
We looked at Magnets and liked their inframe timber shaker Range (the name escapes me). It was a fortune, c13K.
Howdens came back at £10K for something similar. Benchmarx were less again at £8.5K. All inframe shaker.
Although I've not ordered it yet, I'm going with diykitchens.com I found them from a recommendation here and they came out at around the £6.5K mark. So considerably cheaper.
My builder was a little sceptical of buying online until he mentioned it to a friend of his and it turns out he bought the same kitchen we were looking at from them. Builder now suitably impressed so we've ordered a couple of door sample to check the colours.