not sure how much they cost etc. cause i get stuff at trade price, however, when i replaced one a few years ago it was about 30-40 quid iirc so proberbly looking at 60+
i do think vw do a service kit type thing with all new seals etc in so could try stripping it down and re building with new parts.
could also try jacking it up and using a pair of mole grips or simelar to move the hand break lever while spraying with some wd40 or some cleaning agent to try and remove any muck/rust etc. worked as a temp repair on mine for a few months prior to replacing the caliper