For Nema17 steppers with Pololu/Stepstick drivers at around 1A I use WIckes 0.2mm (1.4A per core rating) stranded alarm flex (12.49 for 30m) and pull out the cores I don't need, individual wires crimped with the appropriate pin (dupont, JST, etc) and inserted into a suitable plug.
For Nema 23 steppers with 2-5A drivers I use 0.5mm CY 2184Y 4 core flex (3A per core rating) available here for 0.48/m or £16.25 for 50m, also available in other cores/sizes and Chinese 'aviation' 4 core plugs and sockets from 'the bay' (thicker cable won't fit the cable grip on the plug).
0.75mm flex is rated to 6A per core.