The market will quickly adjust to the point where spending $50 on tokens will on average give you a vulnerability valued at $50. Maybe $100 to account for your edge in having a better prompt and the risk of prison time you take in selling the exploit

In fact that may well be true today. OP didn't try to sell it to discover the true price the market is willing to pay. And we all know that "somebody paid $$$ for something similar in the past" is no guarantee that somebody else is willing to pay any significant sum for your thing today. If it was, startups would be a lot easier