I do web/mobile development for marketing agencies who don't have the budget/workload for a full-time developer. I'm typically handed a set of Adobe Illustrator

I do web/mobile development for marketing agencies who don't have the budget/workload for a full-time developer. I'm typically handed a set of Adobe Illustrator files and it's my job to use those to build working websites/apps. My first project was for $800 in early 2013. The last three years have brought in an average of ~$55K per year. I have several subcontractors who can help out when the workload gets too much, but 80%+ of the work is done by one person (me). A few years back I started offering "maintenance plans" on the websites (which basically entails updating the WordPress core/plugins and giving them a few hours per month for enhancement requests). These are remarkably "sticky" and most clients have continued maintenance for 3+ years. The self-employment taxes are brutal, but it's still worth it.