On eBay firefly's are selling for $80 aus.
So about $96 us. dollars.
(as of 20-9-09)
I get mine at wal-mart or target. They have nearly every kind.
maybe because they are suppose to be everywhere
You can't get it in a store, but some websites have them; such as toys"r"us.com.
If you mean just the store, a lot, a lot of money. If you mean the company of the store, even more than a lot, a lot of money.
Not very much. Most pet stores buy them from large distributors who are able to sell many mice for cheap amounts. The more the store has to pay for the mouse the more it has to charge for that mouse....