How about "It costs $1000 to submit a bug bounty for approval", and raise the reward to $2000 (or $5000 if it's in the cards, since that will have a deterrant impact on non-AI responses).

Denominated in BTC to avoid chargebacks etc.

I think that's entirely sensible. Doesn't even have to be that expensive, just expensive enough to deter people who go "oooh, free money", and expensive enough to compensate for having to review slop far enough to realize it's slop.