I had mine refurbished - only cost around £30 and the work was done there and then, that way you get to keep your original Bosch genuine alternator. These things are built to be refurbished, it's a false economy buying a brand new one unless you are replacing it with a genuine item.
Don't know where you're located but I'm in Redditch and I go to auto electrics by the firestation for all my electrical issues.