When I worked at a bureau, we had a running joke... When a meeting planner asked, "How much is so-and-so speaker?" We'd reply, "What's your budget?" Coincidentally, that was how much the speaker was. Regardless of how much we knew the "rack rate" of that speaker was.

During the 2008 election, Rudy Giuliani was running as a Republican nominee. When his financial disclosures came out, he surprised everyone with how much he made on the speaking circuit. News orgs filed FOIA requests to see what universities and public institutions paid him to speak.

For some events, he'd speak in the same city to different groups. The price each group paid was wildly different (+/- 50k). The meeting planners hit the roof.

Speakers bureaus do not view meeting planners as their clients, the speakers are.