Mecsoft isn't doing this to "gouge" their customers. When the program their CAM module plugs into is upgraded, they have no choice but to modify their module to work with it. And when they do all the work of developing a new version of their software, they feel they deserve to get paid for it. If you don't want to upgrade to the latest version that's compatible with Rhino6, why not just stick with Rhino 5, and the RhinoCAM version that works with it? It doesn't sound like you need any of Rhino 6's new features, if you're just using it for 2D work.