Budget around $50.
Question, before you reassemble the head to the block with the new gasket, how thoroughly do you clean the mating surface on the block and the mating surface on the head?
Do you scrape off every single last bit of your old headgasket off the block and head?
As a rule, I clean both with acetone/thinners and a white rag, until you cannot see anymore dirt on the white rag when you wipe it over the mating surface on the block & head. They really need to be that clean.