Just to get you started, I would recommend you throwing away that idea of building your own cnc from scratch. It's not that great of a idea, no offense. I would recommend you buying a old industrial sized knee mill "which some of these older mills can hold tighter tolerances then these new ones straight from the factory" and retro fitting it with a centroid or ajax controller, or something similiar. I would also only use a precision ground ball screw and for motors here is the specs on a servo that I use on my big mill 110 volt DC at 15 amps. That is what my big mill with servos is equipped with and it runs very smoothly and you can barely hear the motors even running. So in my opinion your going to need to spend anywhere from $1000- $4000 on a mill and $3000-$5000 on the controller and maybe you can throw in the motors all wrapped into that price if your lucky. That is if your looking to do quallity work in steel or stainless steel. If you just want something to make mediocre hobby parts out of wood and aluminum then you can probably get something for like $2000-$6000 brand new no work involved, never spent so little on a brand new machine my self and never plan too. All I see for that price in my opinion is garbage, but to each there own. You will most likely find guys on here telling you that you can go to Harbour Freight and buy some peice of crap for $600.00 and you'll be set up right, thats a pipe dream and you'll wish you never spent a penny on it or even heard the word cnc. This is from my experience that retrofitting a manual mill is the way to go when you not looking to spend $100,000-$200,000 on a brand new mill. And you can come up if done right with a retrofitted mill that can do the same work as those $100,000 mills can.