Gas Cost Function

Some operations and their gas cost:¹

Operation   	Gas     Function
step 		1 	Default amount of gas to pay for an execution cycle.
stop  		0 	Nothing paid for the SUICIDE operation.
sha3  		20  	Paid for a SHA3 operation.
sload  		20  	Paid for a SLOAD operation.
sstore  	100  	Paid for a normal SSTORE operation (doubled or waived sometimes).
balance  	20  	Paid for a BALANCE operation
create  	100  	Paid for a CREATE operation
call  		20  	Paid for a CALL operation.
memory  	1 	Paid for every additional word when expanding memory
txdata  	5  	Paid for every byte of data or code for a transaction
transaction 	500  	Paid for every transaction

[1] https://www.cryptocompare.com/coins/guides/what-is-the-gas-in-ethereum/