The cost depends on the components you choose. Picking cheap components, and being careful, you can probably do one for ~US$500 (rough guess).

That machine would last several years. Though hobbyists do tend to upgrade their machines over time (eg add a 4th axis).

> And if you are just cutting sheets of wood or plastic, you don't really need a proper CAD package.

You might be surprised what you can create from MDF sheet, and/or 2-by-4" offcuts. :)