It is going to depend entirely on what you plan to do with the cnc. Basically the most you can get out of any hobby cnc is some mild work on aluminium (This is at the extreme end and you kind of have to have a very good understanding of machining to get something like that to do anything that is hard.)If your serious about machining metals you have to spend the cash and or understand the processes behind it to DIY it.If it is just for soft materials it again will require some understanding to begin with. As you learn more you will break and or muck up less things.