rust in the bilge from a bolt...
Its a little hard to say. Depending on how experienced the yard is, how the keel is installed, how well the caulk adheres between the surfaces, and what they find when the keel is dropped (i.e. such as glass damage, or bad keel bolts) the price can vary quite a bit. I had a 25 footer done for something under $400 by a yard that does these things pretty routinely. That would be an exceptionally low price as the keel was not adhered at all and they gave me a professional discount since I was still doing yacht design in those days and also had been managing a project they were doing on one of the boats that my Mom had imported.