First $1,000 (and first $100, since it was a $1k contract): I made multiple semi-popular icon sets for KDE over 1999-2000, posting them all as FOSS-licensed artwork on kde-look.org. About a year into that I got an email from a random small startup, praising my work and offering me a fixed rate contract to do a novel icon set for their product, a GUI-ified backup client for Linux desktops.

Amazingly, they persisted even after learning that I was 14 at the time. My poor parents had zero idea what it was their kid did on his computer all the time; I imagine the conversation where I passed the phone to my mom to talk to their CTO was probably one of the more surreal things ever to happen — to either of them!