Probikekit charge £349 for the Precision pre-fitted to a 105 crank. It's more for fancier cranks.
I've looked at P2M, but I'd pay double that for a new one. I could get lucky looking second hand but there's no guarantee. There's loads of powertap wheels for about that money on eBay, but the service costs and potential repair costs put me off big time. Stages are expensive and of questionable reliability, though the newer versions seem OK. Garmin and powertap pedals are silly money. Powertap's chainring solution is more reasonable, but the chainring choice is a limiting factor, particularly when looking second hand, plus I'd need to source some 5 arm cranks.
It looks like bepro or precision, really! If I had more cash it might be a different story. Maybe next time! Hell, power may not even work for me, so maybe best to go in at the shallow end.