fix the head gasket or replace the engine?

would be cheaper to replace gasket but if you can pick up a low mileage used engine I would go that route.

HAVE YOUR MECH GIVE YOU AN EST BOTH WAYS. HEAD GASKETS ARE CHEAPER UNLESS THE HEAD HAS CRACKS. YOU KNOW HOW YOU HAVE TAKEN CARE OF YOUR CAR,BUT YOU HAVE NO IDEA HOW THE USED ENG WAS TAKEN CARE OF