For motor cabling I would suggest Stuttgart Oflex cable... available from Kevin at Marchant Dice in the UK.. search ebay and you'll find their store. The cables are numbered internally, which helps a lot with wiring and are appropriately shielded.

Your talking about doing the job properly.. there's no way unsheilded extension lead cabling equates to this...

You have 2 choices with building CNC really... try and do it on the cheap.. and cut corners... which usually means poor/problematic performance or bear the pain and do it properly. 18 months ago I was where you are now.. asking same kind of questions etc... there's only one approach to take IMHO and thats do it right from the word go.. then you'll have something you can rely on.. and be proud of without any if's or buts.

It always costs more to do it twice than it would cost to do it right... a thing worth remembering ..

regards