Priority (prepaid boxes) are $10-$15
A non-prepaid priority box with the betta in a cup, will be about the same price.
I would definately try to find some 'Bag Buddies' or similiar product to tranquilise the fish for shipment.
Another good idea this time of year is heat packs. For 2-3 day priority mail (fine for bettas), the 72-hr one is your best bet. You can buy them online.
I actually have a lot of bag buddies left over from my shipping days, if you don't want to buy a whole bottle. Kordon breather bags are also good for shipping fish, but not really that great for bettas. (they add oxygen to the water, but don't work well if you leave air in the bag... and bettas need air, as you know.)
Now, overnight express mail (1-2 day) for 1 betta in a cup will end up being less than $35, and it depends on how far it's going. Sometimes it's ok to say $35 to everyone, but some people don't mind giving their zip code for a lower rate.
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