It looks like the St. Louis Public e-card gets you three libraries, once you get the St Louis Library card supposed to also grant access to St. Louis County Library and the St Charles-City County Library. So there’s a large selection. Says this changes it to 180,000 eBook titles, and 43,000+ audiobook titles. (see here:
https://www.mylibrary.org/read-listen-watch-play) This is the one that wanted the 40.00 donation.
It doesn't look they are combined into one Overdrive account that I can tell, though.
At the top of the overdrive account it says Partner Libraries, and drops down to include the other 2.
https://stcharles.overdrive.com/
Not sure of duplicates of each, of course.