I'm very Pro IntelliCAD as a cheap alternative to CAD but you have to check out DraftSight it's FREE
DraftSight: Free CAD software* for your DWG filesYour software. Your vision. Your community. Free CAD software* available for Windows®, Mac® and Linux®. A new 2D CAD product that provides professional CAD users, students and educators with a better way to create, edit and view DWG files.
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