I have had a few open source projects with around 250k installs (web apps and Wordpress plugins). One of them I was able to monetize for about $1k per month. I was getting inundated with support requests so finally I created a "product" by putting up a "buy now" button for $250 installation support. I then ran some google ads to promote it. This was an encryption product so it had business users.

If you make it easy for people to give you money and you have a useful product then there usually will be a small percentage of users who will pay. But I'm a firm believer that to make money you have to put effort into sales.