It kind of depends on what you are trying to do with it. There are so many CAD programs and new technologies out there that I can’t even keep up anymore. If you want to make some simple 2D profile sketches you can probably find a free one. You can probably find a free 3D modeling package too.

I’ve been using software called Solidworks for the last 18 years and although it’s gotten way more powerful and way easier to use I’m not sure if it fits into your “relatively easy and cheap” desire.

I did a quick google for you - http://www.hongkiat.com/blog/free-cad-software/

I can’t vouch for any of those, but there might be something that works for you