LightInTheBox offers four USB Night Light Touch Switches for $1.99 plus 50 cents for shipping. That's the lowest price we could find by a buck. It features two colors.
Note: This item ships from China and may take two to five weeks to arrive. Uncheck "Add Shipping Insurance to your order" during checkout to remove the 99-cent fee. Also, the countdown timer on the product page does not reflect an actual expiration time and resets daily.
If you aren't using any of these three methods for significantly saving on laundry detergent, you are washing money down the drain.