Oh, and... What leads you to think "Head Gasket?"
Oil in coolant? Coolant in oil? Coolant/Oil going out the tailpipe?
6 cyl or 4 cyl engine?
Do you need to pull the engine to change the head gasket? Can you dedicate a weekend to muttering, cussing, and skinning knuckles? This is NOT rocket surgery, and the magic thingy under the car's hood is not actually magic. A head gasket and the stuff to do the job (like tools...) will probably cost under $500.
Google, youtube, find a couple of friends, get some beer, and have a learning experience. Take pictures. Take video. Document everything. I use a big white table and baggies for little parts. Take your time, be patient, and a hammer is not a precision instrument. There are a surprising number of neanderthals in the mechanicking business, and they somehow stay in business.