Just charge the same amount a normal ad clicking (or viewing) user would make you in revenue. I doubt it's more then 1€ per month. On Youtube, depending on you

Just charge the same amount a normal ad clicking (or viewing) user would make you in revenue. I doubt it's more then 1€ per month. On Youtube, depending on your source, you get from 1-4$ per 1000 views. It's not the users problem that payment for micro transactions doesn't scale.