Bill in Houston from Houston on 9/24/2021 9:43:26 AM:
Assuming you're flying into STL, I'd rent the ebike at the bike shop along the waterfront in St Charles.
Then either get a shuttle or take the train west, and then ride back.
Or, if you are starting in KC, a one way car rental from STL to KC might not be horrible.
I know car rentals have gotten a little nuts, but when we did the GAP, renting a car was just a few bucks more than taking Amtrak, and we didn't have to worry about all the Amtrak drama.