I also built https://github.com/nfriedly/node-unblocker around the same time, it's a web proxy for evading government/corporate/school/etc. filters. When I had a copy of it online, it got a lot of traffic from around the world, and used to earn anywhere from $10 to $100/month from adsense, depending on the month. However, it wasn't worth the effort of keeping it online due to abuse + clueless sysadmins.
Unblocker also earned me a consulting fee a couple of times from folks who wanted help integrating it into their project, and I ended up converting it from a standalone site to an Express middleware to make that easier.
Nice site by the way
And, looking at my history, "$20-30" is accurate for the past few months, but it was lower further back. This is the past 12 months, starting at July 2015: $12.41, 4.40, 21.29, 16.12, 13.38, 12.96, 15.56, 11.52, 23.93, 26.04, 23.84, 30.56.
It's been online since 2011 and more or less trending upwards, but last month was the first time ever to break $30.