Sounds like big bucks alright, 3 time was it?
when you have the head off (that is if you are doing the work your self ) do you get the head checked for trueness or have it machined, because if not that could be the cause, also check the cooling system radiator/water pump and hoses, oh almost forgot get the system pressure flushed if the car runs even a little hot, next one is to look at your driving if you drive the car hard it could also cause problems.
Like doing a skid or racing and the stoping and turning the motor off straight away is not to go for the motor. be sure to run coolant in the motor with filtered water as just running straight water is very bad.
Your next step aswell as getting the head checked is also have the cylinder block checked, or just go and get a motor from the car wreckers cost you about $500 give or take depending on availabilty and your type of motor
Hope That Helps You A little Good luck:sun: