I think it's a few bucks, relative to the cost of a house. If you're paying for an electrician, you probably own the house. Compared to the cost of a house, a one-time visit by an electrician is a small amount.

And running wire in a house as it's being constructed is going to be far less expensive than doing it after the fact. I'd much rather add, for e.g., the ability to charge a car in the garage while the house is getting built, than after.