It is hard to tell how much work it is to get this done, as in getting equipment in and setting up for lift. It would seem the contractor has looked as close as he could but there alway could be surprizes.
Your contract with the sell should have them fixing it, the price to be up to them. but if you have settled at the quoted price, it's a little late to worry about it.
As you have moved some stuff in, I think your deal is done and signing the papers is just a formallity.
Congats on buying a house and welcome to the site.