I've used IntelliCAD before, since it can use the same keyboard commands as the older AutoCAD versions out there. I got a copy when they were selling the company, and you could get an evaluation version for free that never ended. I'm not sure where it is right now, since I've changed computers a couple of times since then, and my company provides me with AutoCAD LT (Not very powerful, but it does what I need). You can still download a free evaluation version from their website, but I'm not sure what limitations it might have. You can buy the full standard version for $199.
There are others out there that might be cheaper, but I'm not that familiar with them. You might check Office Depot or Best Buy for a lower priced version. Heck, you might even type "free cad" in your browser and see what you find. I did and found the web page below. IntelliCAD is there, but I couldn't find the free version immediately. Their standard version of IntelliCAD seems to be $149.
Have you used any cad programs before? There's a learning curve with any of them, and finding one that uses commands you are familiar with is a real time saver.