Just the main NFT contract for CryptoKitties, not the auction sale or other helper contracts.
Bonus points if you can also include billable transactions that started from another contract and then did a
CALL into CK.
The gas is not fixed it varies according to the operations in a transaction. Every operation use fixed gas. Please check the gas cost per operation. gas cost
Currently, the standard gas price is $0.026 according to https://ethgasstation.info/index.php
You can change this cost as how much you want to spend on gas. It will affect the duration of verification of the transaction. If you pay more gas price then your transaction will mine very soon and vice versa. If you pay very less price then it might be possible that it'll never mine.
Read this article you'll get a good idea of it Ethereum gas