My room mate had friends over to the house at the weekend and one of them dropped a wooden statue off the mantle piece and it took a big chunk out of the base of the fireplace. It's a granite or marble fireplace and it is rented accommodation (belonging to a mate of mine) and she will need to get it fixed as my mate will go nuts!!!
Any ideas on who to contact, rough estimate of costs etc....
I think you mean the hearth, the bit that sits on the floor?
Start out with fire-place shops, refer to your local Golden Pages.
Cost will depend on whether its marble, granite or some other material, whether the fire-surround is installed over / attached to the hearth and whether the hearth itself is in one big piece or three or four separate pieces (most likely).