How much will it cost to repair a blow head gasket on a 95 nissian altima?

For a simple R&R, the gasket and related parts could run anywhere from $60 to $100.
Due to variable shop rates from one area to another, labor will differ significantly. You could expect labor hour quotes to range from 12 hours or more, depending on what is neccasary to do the job properly. At the rate in shops in my area the quote would run around $1200 out the door. That seems like quite a bit for a car that old, not knowing the mileage or overall condition of the vehicle.