With between 10 -20 thousand active users here (probably diminishing) the math presented don't add up to a long term advertising reality, not as far as I can see...
https://www.quora.com/How-much-do-companies-pay-to-post-an-ad-in-a-popular-website

Matthew Toma, Sales Manager "Cash Quest App" www.cashquestapp.com
Answered Apr 9, 2016...
It depends upon popular "in general", or popular "niche". Popular in general websites with large broad audiences often charge $2 - $10 per 1,000 impressions (CPM). Popular "niche" sites can cost $25 - $75 per 1,000 impressions. So it varies on how big the audience is and how specific it is at the same time.