What to do when I have energy loss due to distance
Everyone seems to be suggesting the thicker wire route here.. but you do have a different option.

Your other alternative is to either use a boost convertor to convert your 12V into a high DC voltage or use an invertor to make high voltage AC and transmit that down cheaper cabling instead. Then add DC-DC or AC-DC power regulators at each motor.

That may seem extreme, but you need to do a cost comparison of which is cheaper. Big beefy hard to manage cables, or cheap wiring and low cost convertors.

The other benefit of this route is you separate the power transfer efficiency issue from the target voltage-drop issue. That is, the system ought to be 100% functional despite the transmission costs.