Have you ever checked out google sketchup? It's free and pretty easy to use. I took a community college course on it and the required text was "Sketchup for Dummies" which is really helpful and inexpensive.
You might ProgeCAD software, they have a free 2D version of their IntelliCAD based cad program and it is a pretty good one. It is free but they ask for a donation to Doctors Without Borders or something.
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