> The cost of the attack would far exceed ~80k USD in bitcoin block rewards because it requires a substantial amount of hashing power to have a realistic chance of successfully producing a block that reaches consensus and is added to the canonical chain.

No, the cost is simply $80k on average to find a block, or around $5k for BCash. If the cost to produce a block exceeded its value substantially, it would be on a whole unprofitable for Bitcoin miners to continue existing at this point in time (network difficulty, bitcoin price).