I've used AutoCAD for probably 17 years at work. In my experience all the drawings we receive produced using cheap or free program's are very poor in comparison. Now if your not e mailing the drawings to others and just printing them off maybe a free program will meet your requirements. I'd love to see a cheaper usable alternative as Autodesk are gypsy thieving barstewards, IMO
I use AutoCaD LT on my Mac desktop and MacBook Air, via parallels. AutoCAD is available for Mac but its eyewateringly expensive.