I am currently at around $300/mo so still a bit off the $500 unfortunately. My side project, ErgStudio[0], allows people to use their rowing machine to do remote workouts together. I had the idea already a while before the pandemic started but when it hit I finally pushed myself to implement a MVP. My wife helped a lot doing the admin and as a photographer (we took all the promotion pictures ourselves to save money). This was also the first project for me which I took from greenfield to people-can-pay-for-this, which I am pretty thrilled about. At the moment, a bunch of university clubs in the US and smaller rowing clubs in Europe are using it. As a gimmick, when you see the meters rowed counter changing on the website, someone is actually working out somewhere in the world, using our app.

[0] https://erg.studio/