A lot of marine electronic suppliers will have second hand handsets, Greenham Regis in Lymington will i'm sure, but obviously it may be cheaper if you can find one on here.
There is a "wanted" section on the forum, if you haven't already done that. I'd have thought you're looking about £40-£50 on here, £70-£80 through an electronics supplier.
Take it apart and clean in with fresh water then put it in the airing cupboard, it may live again. However, if the 12v was still on then it may take a bit more to jump start it again.
I had to buy one about 18 months ago and it was £150.00! to be honest, if I had another one go defective I would buy a new dual system, as they've really come down in price.
If you're really intent on buying one, I'll try to find my original receipt. Just PM me if you need to.