The idea was to use a single sheet of hardwood plywood, and some basic hardware to build this desk for between $75 and $100. It could probably be built for less if you changed some of the materials.
Unfortunately I didn't document the build process at all, so I only have pictures from several years after it was built, and some pictures of a much larger version that I built later. I've included pictures of the other desk (a similar design), and the completed desk as it is today.
Step 1: Planning
I laid my desk out on a sheet of graph paper using a 4 squares per inch rule.