20,000 gas for 32 bytes of data if you want it to be accessible by other smart contracts. 16 gas per non-zero byte (4 gas per zero byte) of "transaction input d

20,000 gas for 32 bytes of data if you want it to be accessible by other smart contracts. 16 gas per non-zero byte (4 gas per zero byte) of "transaction input data," which is accessible to clients off-chain but is not accessible to smart contracts.