How about put the pot 500,000 credits at first then take 5k off the pot for every wrong guess. Meaning if the first person guesses the song exactly right, then that person is not only lucky as f**k, but rich too. Also that will ensure that there won't be a winner every single day, but like once every 3 days on average. The amount of guesses per day is fine though.

Also I want to throw in that it should cost 5k per guess per account per IP address so that for one: Credits are actually spent, and two: Nobody make alts just to try to guess three more times after transferring credits to that account.