I never played any games like that, but simply giving the agent a clear exit criteria and instructions to check the exit criteria every time it thinks it's done on a complex task was often enough to keep it chugging away for most of a day on a single prompt in my experience. Per-prompt pricing just isn't sustainable period, even if everyone is acting in good faith.

Charging by prompt was always wild to me.

I once asked it to do a comprehensive security review of our code. It churned for nearly an hour (and then produced 90% false positives). Insane that that usage was charged the same amount as me just saying "Hello".