How much does it cost to repair frozen pipes in an existing house?

Between $50 and $120 per hour plus truck and parts charges. Overall cost depends or severity of issue.

Unless you want to call him back, have the plumber install heat trace. It is essentially a heated wire that gets plugged into the wall and wrapped around the pipe so it wont freeze. If pipes are freezing they are most likely installed wrong by Plumbing Code. Check with the City or County to determine the installation requirements at the time of construction. If said frozen pipes are in the original plans, then it's the city or countys fault since their inspector allowed a faulty system to be installed.