I've found the solution. In order to generate keys for individually priced download channels you need to use the Create key group button and bulk generate however many keys you need rather than trying to generate individual download keys. You'll be given the option to input what dollar amount the key(s) grant access to. In my case it's one key with a set price of $, granting access to the $-tier paid version of the game.
I'll leave this thread up for anyone else confused about the same thing.