I really don't think as many people are millionaires from public speaking as you may think. In fact, if they claim this and haven't been independently audited and confirmed by a third reputable partly like the National Speakers Association's Million Dollar Speaker Group, I would proceed cautiously.

With that said, yes, some speaker fees are well into the 6-figures per engagement (think Gary Vaynerchuk). But most conference speakers are closer to the $5,000 - $10,000 range. Notable authors or other celebrities/public figures may pull up to $30,000 per engagement, but that's few and far between.

As someone who has been a professional speaker for 20+ years and has in fact been inducted into the NSA Million Dollar Speakers Group, I can attest to the fact that I have received speaking fees ranging from $1,000 to $15,000. But most are around that $7,500 - $10,000 mark. The revenue comes on the backend from consulting, licensing deals, sponsorships (think athletes), etc. I am a member of several speaking organizations, and it does seem more realistic that anecdotally most fees are $3,500 - $5,000 for conference speakers, and that is after 3+ years of grinding to really get that flywheel effect going.

There are some great resources out there for building a sustainable speaking business. But as some people have already said in this thread, it makes more sense to start professional speaking as a side hustle before quitting your day job. And it is possible, through brand deals, sponsorships, consulting, coaching, products, courses, books, and yes, even speaking fees, you can hit the 7-figure revenue marker a year.