Durov recently announced they will smart monetizing through ads, but only in "channels" of people with huge subscriber count (which generates a lot of costs). Channels are 1:N public broadcasts, a bit like Twitter.
$1 per user/year sounds about right. I use Telegram more than any other chat app. People send lots of media (and even large files) and Telegram archives them forever. One group Telegram I’m in is 6 years old and has 500+ VIDEOS (and 10,000s of images) permanently archived in it.