I suppose that will depend on the going rate your way, my own '98 outback wagon blew both gaskets and i took it to the dealer to get it fixed. 1600$ later i got it back.
The tires, fuses, gaskets, pipes, transmition, and engine. Aslo you should ask the previous owner about the mileage.
it should be changed every 100,000 miles
It is not necessary to change those gaskets if all you have done is change the knock sensor. If they seem to be worn then you probably should go ahead and install new ones.
i should be inspected at 120,000 miles or 193,123kilometers then the mechanic will tell you if it need to be changed
The heads don't necessarily need to be resurfaced when you change the head gaskets unless you think they may be cracked. They should be resurfaced every time the gaskets are changed, but you can get by without resurfacing them.
It is advisable that you check with your local mechanic as to when you should get your transmission fluid changed in your car. Ideally, it should be changed every 3 years or so if the car is driven aggressively.
A mechanic old me about 100,000K
Your Mechanic should do this complicated Job. But if you want to DIY it then start [http://www.themotorbookstore.com/malibu.html Here] Hope This Helps.
If you changed them yourself it is recommended that you get an alignment done or do the alignment yourself. If a shop or mechanic did the work they should have done the alignment themselves.
2002 Grand Cherokee with the 4.7 V8 engine head gaskets replacement would run aprox $1500 to $1800 parts and labor depending on your location.
I'm a mechanic, And have my own buisness . I charge 350.00 for parts and labor. But my labor rate is only 50.00 a hour, And parts are about 50.00
If it is a 4 cylinder, it will run a few hundred dollars. If it is a V6 or v8, BOTH head gaskets should be changed at the same time.