That should be listed in the car's paperwork when it was signed for and any fees and taxes will be listed on it too, check the glove box and look for it. Mine was around $1,000.

^EDIT:Find out through who was the extended warranty done with. Mine was with Toyota and had mine cancelled when I traded the car in at the dealership(I actually traded in the car at the same dealership it was originally bought).

 

Its totally dependenant on how much your dealership wants to charge, what kind of deductible you choose and how long you extend it for. I paid a little over $1000 to extend it to 6 yr/75,000 miles with $0 deductible. But that was after getting the dealership to knock $300 off the price, I think if I remember right. I had to go thru the dealership I bought the car from to process the paperwork to cancel it.