Transaction cost isn’t determined by hash rate. The difficulty adjusts to the hash rate such that a block is mined every X minutes. Because the block size is fixed, transaction fees are determined by the market for being included in a block, so the more transactions the higher the fees.
An alternative to Bitcoin’s fixed size is Monero’s adaptive block sizing. Monero blocks expand to fit more transactions, resulting in lower fees and higher throughput.
The difficulty doesn't magically adjust right away.
It adjusts after two weeks on 10 minute blocks.
When the has rate drops suddenly as it just did, the block rate drops and the transaction capacity drops with it. The time to adjust also stretches out since it is based on a number of blocks and not on absolute time. If hash rate drops 50%, then the transaction capacity drops 50% and the time to adjust extends to about three weeks instead of two.
An alternative is anything else but bitcoin and ethereum. Those are the only two with high transaction costs. Bitcoin cash, monero, dogecoin, litecoin and whatever else are still viable, although when dogecoin shot up the transactions started to cost 50 cents to $1 USD.
An alternative to Bitcoin’s fixed size is Monero’s adaptive block sizing. Monero blocks expand to fit more transactions, resulting in lower fees and higher throughput.