If you're all about Open Source software, Windows, macOS and Chrome OS aren't for you. But that doesn't mean you can't use a standard laptop for a non-commercial experience. Minifree's libreboot C201 is a $730 laptop that runs exclusively on open source software.
The computer is actually an Asus C201 Chromebook, which costs $300 new on Amazon as of this writing. It runs a 1.8 GHz Rockchip CPU, 2GB of RAM and has 16GB of storage. so it's not exactly a high-end performer. It also features a 1366 x 768 display.
It doesn't come with Chrome OS on it, though, but the open-source Debian OS. Minifree also added a Wi-Fi dongle from Atheros with open-source drivers instead of relying on the wireless card built in to the computer.
If you're OK with using the built-in wireless card and associated drivers, you could buy the Chromebook itself and flash the latest libreboot release on your own. That would save you over $500. But to some, privacy is priceless, and to them, paying the full price is probably worth it.