I know that we keep hearing about Chromebooks and all kinds of very inexpensive computer systems intended for students or people in the developing 3rd world, etc..
You might think that it is impossible to build any kind of computer that you might want to actually use for very little money.
You would be dead wrong about that!
Let's have a look at what 5 minutes of Google searches turned up:
BeagleBone Black rev C: ($55) http://www.adafruit.com/products/1876?gclid=CIiGo4im-r8CFSpp7Aodcx4ALw
Raspberry Pi B+: ($35) http://www.element14.com/community/community/raspberry-pi/raspberry-pi-bplus?CMP=KNC-USA-RPI-BPLUS
BOTH boards for a Grand Total of $200. (Yes I said "less than" - so choose one board)
This is not a pretty design by any means but it will work
Both boards run Debian by default – and you have many options to choose from there.
You could forget what I just told you & spend $300 on just a board that can run Windows: http://www.pcworld.com/article/2459200/meet-microsofts-sharks-cove-a-raspberry-pi-style-mini-pc-running-windows-8-1.html
But obviously, that doesn't make any sense at all.