I think Moss sells an aftermarket A/C kit for the B's now.
I'm surprised you said prices have gone up. I remember seeing them in the paper all the time for 2-3k.
Brutally simple cars, but f'ing Lucas wiring. I've commented that the main wiring harness in the dash is the same size as the wiring harness in the door of our Lexus.
Here's a pic of my 78'
Currently undergoing a neverending upgrade of:
Rover 3.5L V8 w/ BW T-5 trans and Ford 8" rear end
coilover shock on all corners
4 piston calipers and vented rotors all corners