Ah yeah, probably more important to have it then. But probably best to find one with it fitted rather than go to the hassle and expense of retro fitting I would have thought?
I've got a T and even in the winter/cold wet days there is a fair bit of heat soak into the cabin. I've used my air-con quite a bit and certainly wouldn't want one without.
Got a few quotes of £2k for having it done to the Tuscan a few years back. Not a cheap job. Would have worked out far cheaper to sell the car and buy another with A/C.