A bitcoin hash is created by a process called mining, in which computers solve complex mathematical problems in order to add blocks to the blockchain, a public ledger of all bitcoin transactions. The more hashes that are created, the more difficult it becomes to find new blocks, and as a result, miners are rewarded with bitcoins for their efforts.
The amount of bitcoins that a miner can earn per hash is reduced over time as the network becomes more secure and more hashing power is added to the network. Currently, each hash created by a miner results in a reward of 12.5 bitcoins.
However, this number will be cut in half every 210,000 blocks (approximately every four years), until the block reward reaches its minimum of 0.00000001 bitcoins.
At current prices, this means that each hash created by a miner results in a reward of approximately $125. However, as the price of bitcoin fluctuates, so too will the value of each hash.
In conclusion, the value of a bitcoin hash is determined by the current price of bitcoin and the amount of hashing power on the network.