Leaking engine oil, apparently from the head gasket

The car has about 66,000 miles on it. I was thinking it is okay to just top up with oil as needed rather than go through an expensive repair, since it only needs about a quart for about 3000 miles. What could go wrong if I continue to do that? How much is the estimated cost?

Thanks; that's pretty much how I saw it too. The shop mechanic (that inspected the leak and suggested that the head gasket be replaced, a very expensive proposition) said there could be a car fire because of the leak, since it is near the exhaust pipe. That seems so remote, given the amount of leak I am experiencing.