Loonies do seem an expensive option. How about pebbles? It’ll be a few months before any nearby pebble beaches are ice free, but a big box DIY store should carry them. It’s more a spring through fall thing, but it would be cheaper than the rocks at an aquarium store.
Loonies definitively, and they wouldn’t fit. So either 5c or 10c (but I think 10c is less dense for more cost)
I don’t have access to ice free pebbles, so to the stores maybe.
Line it with plastic and pour concrete in there. Cheap, easy, heavy. Done!
if there is a pick-n-pull / automotive junkyard near you, you might be able to harvest old tire balancing weights
I like this. Even plaster of paris or similar.
Perhaps your local tire shop might have old weights they might share?