Last time I bought CO2 was 6 years ago. Got 2x25 packs of 12g unthreaded carts from Wally World for $0.50/cartridge IIRC. Still have over half that lot left.

Nice thing about CO2 guns that fully enclose the cart, you can save and get unthreaded carts, which are more readily available. With the Innovations enclosed inflator you can flip a cart around backwards inside it and have it safe and sealed forever until you need it, saving space for more carts in your saddle bag (or jersey pocket)....also don't have to worry about freezing your hand holding the damn thing.