This plastic bottle cage weighs only 24g, saving up to 35g over a generic alloy cage, or 70g per pair. These cages feel less flimsy than the 25g versions of Generic Plastic Cage #1,
however, the vendor I purchased from no longer lets you pick colors and was unreliable. Unlike the aluminum cage, it will not mark up your bottles as much either. At $1 for two, and saving 70g per dollar, it represents an exceptional value, very low cost upgrade. It was purchased on Aliexpress. You may be able to find them on eBay.
At $3 for two, saving 23.3g per dollar, is represents an exceptional, very low cost upgrade. It can be found on eBay.
Price: $1/pair [Very Low Cost]
Value: 23.2g/$ (0.04$/g) [Exceptional Value]
Recommended with caveats
The vendor was unreliable, and no longer lets you pick colors. Update: I have found what appear to be the same cages on eBay for $1.50 each. Even at 3 times the cost, it is still an exceptional value and a good option. Note that there are two bottle cages that look similar to this one. This one has the heart shaped hole at the top, and the rectangular hole between the mounting holes. I purchased additional ones off of eBay and can confirm they are the same, and weigh the same 24g, although they may have some mold flash.