what kind if help you need? have you done this before? for a robot? robot cables are designed for continuous flexing and torsion with small mend radius. and they are expensive even when you get them by length. then you need to get suitable connectors and tools to assemble them. Crimpers and pin extraction tools are not cheap. and workmanship need to be top. having assembled bunch of cables myself and repaired ones assembled by others i have to say that i do not see a benefit of making own cables unless you are experienced in this and already have tools and some or most of materials at hand or can get them cheap. remember, sum of parts can cost more than ready made complete and tested assembly.
https://www.lappkabel.com/products.htm
as mentioned, simple 2 conductor AWG20 cable is more than $9USD per foot - because it is a robotic application cable.
https://www.igus.com/chainflex/robot-cable
motor cable will have bigger conductors, more of them, be thicker and still be flexible costing even more 
but you can talk to them and see if they would make cable assemblies for you.
following panic modes suggestions:
home made cables are not less expensive (correct type of cable, required tools, proper connection material) but more dangerious (cable length, wrong shieldung, wrong internal wiring) and even more important loosing warranty
