Making one yourself is very limited. It can only do a certain amount of things with very limited x and y axis. Also, you have to directly program it instead of simply using vector drawings. Programs like MasterCAM do not work with it because it uses its own custom controllers. It functions more as a router, as the only metal it can cut through is aluminum, and not much of it.
Sure, it is cheaper, but if you will only use it a couple of times then it would be easier to get a custom job from somebody who has a CNC machine.
Hell, the only reason I have one
is I am self employed, and my business type requires it. Otherwise there is really no reason to have one.