Amazon has a 12 pack of A&R Sports Classic Ice Hockey Pucks for $11.46 which is the lowest price I’ve seen to date. Besides obviously being used for hockey, it is also useful as a jack pad to prevent scratching the underside of a vehicle, anti-vibration pad under an air compressor, LP clamp if a hole is drilled in the center, and whatever other uses you can think of.
https://www.amazon.com/dp/B002D1SHRW