You could record data from the chat, when they sub there is a USERNOTICE
msg-param-sub-plan=1000;
1000 is 4.99
2000 is 9.99
3000 is 24.99
Prime is Prime
Add it to a database/text file with a date/time stamp or something, and set it to remove it in ~30 or so days. It should keep the list fairly current but the bot would have to be active 24/7 to stay current.