Lots of people try chemiweld but I'm personally not a fan of those "stop leak" products. And considering its the headgasket you have a 1% chance of it working for maybe a week. These additives are more designed to stop a leaky radiator not headgasket.
To remove the engine and replace the head gasket most places would be quoting in excess of $1500.
Where are you located? I can help in Adelaide for a much better price

Built not bought, it's a way of life.