Can anyone recommend an inexpensive (of free) program that can make electronic mods on a drawing.

I'm working thru the final stages of a 1 year long commercial project and part of the specs require for me to submit as-builts. I have several penciled diagrams of how things were done but we'd really like to impress the GC with a clean set.

I've used AutoCAD before but just need a program that can add basic lines to a floor plan.

Any rec's?