The network cost / miner fees, the "block reward" is essentially a revenue item for miners, and a cost item for the Payer.
It usually compromises both inflation (newly "mined" coins) and some form of transaction fees.
Typically, miners choose which transactions they want to include in each block, based on how high their transaction fees are. The higher the transaction fee, the more likely the transaction is to be included and eventually confirmed in the blockchain.
Transaction fees are the "most visible" cost that everyone participating in the network can experience. Transaction fees have historically been incredibly small for each peer participating in the blockchain world, though with scale and more users, we have seen transaction fees rise overall.