If the vulnerability is already being exploited in the wild --- as in, it's a vector people already know about and are tracking --- it's possibly not worth much at all. Vulnerability valuations depend heavily on the lifespan of the vulnerability; payments on black market are tranched (explicitly or less explicitly, as with "maintenance payments") based on whether they're patched.

Further: a vulnerability is probably not worth that much either, even if it's a hypercapable vulnerability, because the grey market buys full enablement kits, not vulnerability information. People making 6 figures on vulnerabilities are selling fully enabled full chain exploit systems, not just intelligence about a sandbox escape.