WElcome to the forum Rachel. The alternator is not that easy to get to but can be taken off and changed in about an hour. I've just done mine this morning and took some photos so I'll do a "how to" and post it.
with mine it was the brushes / voltage regulator assembly, spent a day calling round but not available from suppliers. I ended up getting a price for a recon of £119 so I picked one up from a low miler at a scrappy for £20, an hour later and job done.