It also depends on the type of nesting that you are doing. If you are cutting many sheets of expensive material, in the same pattern, a human being will almost always produce a better nest, utilizing less material, than even the most expensive programs. I recently spent nearly a week nesting some parts to be cut from fabric and tape via a laser (only 2 different nests). I also sent the same parts to all of the nesting software places I could find that looked like they may have a shot at doing better ( about 6 firms ). The closest utilized 20% less material than I did. At the cost of the material savings, I could have spent a month nesting the parts, and still come out ahead, although after a week, my sanity was fading quickly.
If your material is not expensive and have to do many different layouts, but can't justify much investment, you might take a look at this software. samtechindia.com. Their demo software is semi-funtional ( limited to 3 shapes I believe, and possibly the # of degrees of rotation that it'll check). Howver, it does export a .dxf, and is free.... free is good.