Belkin doesn’t sell the Secure Holder with Key Ring for AirTag in Singapore; at least I haven’t come across it. The closest I could find is the Belkin Secure Holder with Strap for AirTag which Apple Singapore is selling for S$19.15. In case it is not apparent, one is a key ring, and the other is a strap. The holder itself is the same.
One is the Apple AirTag Polyurethane Loop (or, in short, AirTag Loop), and it comes in for colors, Electric Orange, Sunflower, Deep Navy, and white. It retails for S$45, or if you are on Apple Corporate Employee Purchase Program (EPP), it is S$40.66.
If you find the Apple AirTag Leather Key Ring too expensive and you don’t need the luxury or premium touch to your keys, you can consider getting those OEM AirTag Key Ring.
I bought two from Shoppee and they only cost S$3.32 each with shipping to Singapore an additional S$1.