My sugestion would be to purchase the best electrics (controller, motors, powersupply) you can get, as you will certainly be building more machines.
Also Ball screws seem to be overkill for a MDF based machine. That is unless you plan on using them for your next machine as well. For this machine you might be better suited to using ACME screws. Take the money you would spend on the ball screws and purchase a better electrics kit like the one from CNCrouterParts.com.
Later when you build you next machine you can look at upgrading to ball screws or R&P.