I bought a Toshiba CB35-B3340 13.3 Inch Chromebook/4GB RAM for $269. It has a really nice 1920 x 1080 display.

Then I installed the SeaBIOS firmware from John Lewis, https://johnlewis.ie/custom-chromebook-firmware/rom-download...

Then I installed Ubuntu 15.04.

Everything works great, including the HDMI adapter, wifi, sound, webcam, USB, etc. Accelerated OpenGL and WebGL works, although the performance isn't going to win any speed contests.

The thing only has 16GB flash storage, which is a little small so I added a 64GB compact flash card for more storage. Otherwise it's a great cheap Linux box.