I think mine's on it's way out too, mine is more like a squeal, it's only at tick over/low revs though, hold it around 2K and it goes.
You could try some WD40 etc around that area, it's hard though to get it past the clutch area, it does help with the noise for a while.
I'm guessing they could be reconed if you can find someone to do it, the unit looks easy enough to remove from the engine bay, well on the 2L. Of course you have the gas in the system to take care of first, you should close the ends off any hoses/pipes if the system is going to be left open for some time.
I had a quick look at the manual and it does looks fairly easy to remove the compressor. It seems to be a fairly common model used on lots of cars as well so half a chance of picking up one cheaply:
Only confussion is some are marketed for Ford, some for Rover, some for Peugeot. Will there be subtle differences in mounts etc. or will they all be exactly the same?
Price seems to vary from £98 up to £250 for a new one depending on the brand of car it is being advertised for! If they're all identifcal I'll take an old stock Rover part for half the price!
I may try the WD40 route first, but mine is making such a rumbling noise I think it is likely one or two of the ball bearings have completly imploded which no end of WD is likely to help...
On the gas front, I'm taking it for granted you'll loose it all in a switch, therefore is their any point plugging the ends - i.e. I'm assuming no damage can come from loosing it all (to the car at least - sorry O zone)? As the system is pressurised the majority of the gas will be gone the second the hose are unscrewed.
Any more thoughts out there?