How much does it cost to refill a Co2 tank?

$3-$4 bucks depending on size

At most Sporting goods, gun, and paintball fields. Some Gas (not just gasoline, but Ike propane) places you can fill your CO2.

21.

Depends on how you want to purchase it, many big department stores sell it, the big one that starts with 'w' has it.

$100,000,000,000