FWIW When I was a student at the Art Institute of Atlanta, one of my instructors was Aarron Walter (UX Lead at MailChimp). He mentioned they paid John Hicks a flat fee of $50,000 for the logo and the monkey illustration.

For them, building on the emotion and branding of Freddy was not a joke and they wanted something that could be playful while still performing an essential business function.

Agree with the cost or not, it did start an era for them where they've done very well.

I imagine Jessica's fee was not as much as Hicks but not far away either I'm sure.