How much should it cost to replace head gasket

I took my car in because I wasn't getting heat and temp would go high but not into the red area. They told me that I needed a new intake gasket. It would be about $700. I didn't have the cash and they said go ahead and drive only when I had to and keep the coolant filled and check each time. Today I took to get it fixed, they now say I also have bad head gaskets. The price if now going to be $1900. Said the cooland was in the oil when they checked it. Do you think this is a fair price? Why woud this have happened?