electrical fire rewire

We just bought a house that has had a small electrical fire. I plan on calling an electrician to do the work but im looking to get a little more information before I go that route. The wall has been exposed where the fire has started. Im assuming partially due to the fire itself and when the fire department came and inspected. It took place on a step landing going to the second story. Will I just need that line rewired? Im not sure of code but i was told that I can still have the older wiring as long as its in good condition. Obviously some of it is not. Would i need the whole house rewired? and at a rough guess how much is that going to cost?