Links to that actually happening *for non government officials* is exactly the kind of evidence I'm asking for.
Here's an article about them: Matthew Mcconughey got $135k for one at the University of Houston; Katie Courik got $110k for speaking at the University of Oklahoma in 2006. Crucially, the article notes that a) fees are often confidential, but can go up to half a million dollars(!) and b) schools try to bargain them down.
https://www.insidehighered.com/news/2015/04/02/matthew-mccon...
Many universities also have "lecture funds" with pretty hefty budgets. I was not privy to the exact numbers, but assuming they run at cost, ticket price*capacity suggests some people are commanding six figures.
Edit: here's a link, since it only takes 10 seconds to find: https://www.allamericanspeakers.com/discover-your-speaker.ph...
Notable: Ava DuVernay (film director) starts at $200k. Tim Ferriss says $100k-$200k. Viola Davis: $200k and up. I'm certain that none of these people are obligated to these prices; if Citadel is buying, anyone would be silly to not raise the price. Conversely, all are certainly able to make speeches at discounted rates or gratis to schools, nonprofits, etc.
Also notable (because it refutes your priors) is a lack of public officials, or those who have held public office.
Edit (again): Here are private economists who make bank for speeches: https://www.allamericanspeakers.com/searchresults/economist#...
Sort by price and you'll see that people do hire economists to speak for six figures, even if they have no nexus to government. Yellen is higher-profile than most of these, and again anyone would be foolhardy to not double their rate for Citadel.
Here's Dan Schulman at Goldman Sachs: https://www.youtube.com/watch?v=4q_jVu5T80g
Or at a conference that runs $2300-$7000/head: https://www.youtube.com/watch?v=4q_jVu5T80g
This is admittedly a little bit murky, since some of these appearances might be part of the person's "day job": Helmut Panke talked at a bunch of auto shows about BWM and its new products. The ones I linked above, however, seem like they're probably not.
Links to that actually happening is exactly the kind of evidence I'm asking for.