it is a major job. I have fitted the control panel and associated parts (centre console, housing etc) inside the car including all the wiring. I still have to fit the aircon side of it! I do have the rest of the parts apart from a pipe still to get, once I get that it will be ready to be checked and gassed (in time for summer!). Cost is hard to say, i got most parts off of ebay and breakers. Must be about the £500 mark by now. Probably better if you got it off one car all at the same time - I got the whole airbox including motors and evaporator for £27 of ebay and then spent £30+ on the sunlight penetration sensor!
I did it as much for the challenge - nobody else had done it and most said it would be too expensive too, but its the same price as a remap. When it gets a bit warmer I will be fitting the pipes,compressor and condensor.