If you have a cast iron block and an aluminum head, the block and head expand and contract different amounts and at different times as they heat and cool. The head gasket has to tolerate this relative motion. Under ideal conditions, the head gasket will tolerate this for somewhere around 15 to 20 years of daily heating cycles. Then it has to be replaced. It is not a bad design, just was not designed to last forever.
If the head gasket is that old and it is just leaking water or oil to the outside, and the car has not overheated, there is no reason to suspect a warped head so the job is a simple R&R.
Why $2k? What kind of car? I replaced the head gasket on my '91 Volvo last year (260k miles). Total bill was about $100, including the 1/2" breaker bar and the socket that I had to replace because I broke them. Those bolts were really tough to break loose. I spent all afternoon and evening doing it, but most of that time was cleaning out vacuum ports and other stuff that is hard to get at with the head in place.