Indeed I would
I just cannot see how it's possible to go from stock (or even base BPU) to a complete single for less than £5k. You could get very close to it if some budget items are used (IC, cats, exhaust for example) AND it's a DIY install, but using new branded parts the figures don't add up.
I'm in the process of writing a single conversion parts list using several different options (cheap as possible T61, 'normal' T61, 'normal' T67 and high end T67), none of the figures are coming in below £6k so far provided you're going from stock or BPU spec.
However I do not think this is so relevant to Imi's thread since knowing him he'll want a plug and play install & mapping that will not be DIY.