(b) There are other prizes, but I'm not aware of any others worth a million dollars. Do you have any pointers? A quick interwebs search didn't turn up anything, but they might just be being swamped by the results with the Millennium Problems.
Searching 'collatz conjecture prize' quite literally puts a prize of a bout 120MM Yen (~ $1MM) as the top result.
Thanks.
<shrug>
Thanks for finding this and letting me know, I've learned something.