Unfortunately, you will probably find most CAM software expensive. My personal recommendation would be to start with Rhino (Modeling tools for designers) and madCAM (MadCam Start page), and once you have some revenue, maybe move into a parametric software like Solidworks and one of it's gold partner CAM applications. At that point you will need to invest over $10K for sure!!
This is a topic with no clear-cut answer. Others will no doubt have other recommendations. It's like asking "what's the best car?", or "what's the best religion?". What's "best" for some won't be even a consideration for others. However, you did specifically ask "best for the price" so the Rhino/madCAM combo would meet that criteria.
Hope this helps,