I run a few projects for ~$400 MRR. Here's my numbers from last year: https://www.simonmweber.com/2019/01/07/side-project-income-2...

Since there are questions about company formation in the comments, here's my notes on US taxes/legal from when I got started: https://www.simonmweber.com/2016/07/11/launching-a-chrome-ex...