How much does it cost for an electrician to convert one ungrounded socket into a grounded socket in my house?

My room only has two-pronged outlets and I was wondering how much it would cost for an electrician to convert the outlet into a properly grounded 3-prong outlet. Is there a lot of work involved, such as going underneath the house or tearing up the walls? For one socket, how many hours of work would it usually take? What would be the cost of such work? -Thanks!