As someone who doesn't earn quite as much, whose day job is maintaining and modifying big, monolithic and outdated Spring/Webflow/JSF applications from hell I'd like to ask you: What exactly are you doing and how do did you get there?
Sorry for the late reply, I work in integration. I say I'm a Java dev but I don't write much Java, I've specialised for the past 3 years in an ESB called Mule.
The need for the tech seems to be rising around the world and I just happened to pick it up on my first job (have been working "professionally" for 4 years). Didn't really start fully understanding the quirks and good ways of doing things with it until this year, but I was charging $80/hr 2 years ago.
Seeing as you're already familiar with monoliths, I don't think it would be a very far jump for you if you were interested in the tech. You can get certifications for <$200USD with Mulesoft (a unicorn startup) which would guarantee you a decent salary, contracting on the other hand is a networking game.
Write a blog, give talks, goto meetups and find companies that need your skills. Don't undervalue yourself, if you set your rate too low - your clients aren't going to like it in a years time when you've realised you're worth 2X and you start charging them 2X.
