You cannot and should not buy a used head gasket. If you have a blown head gasket you replace it with a new gasket. The gasket will cost very little. The labor to replace the gasket is where the cost is. Expect to pay from $500 to $1,000. This is a major repair that takes time.
All head gaskets are located between the engine block & the cylinder head. In theory you do not need a head gasket if the head and block are perfectly machined but in practice, a gasket is normally fitted as the cost of such engineering would not be cost effective Best wishes
It depends on if you have been driving it with a bad gasket. Most garages will have to send out the head to be tested to make sure it is not warped. I had a cracked head gasket but the head did not need to be machined. The repair cost me $750.
Depends on where you live, who performs the repair, dealer or independant, and if the head is warped or cracked. The head gasket will for sure have to be replaced and then the problem that caused the head gasket to blow solved. It can cost as little as $800 to as much as $3,000.