Get a box that you think would hold the fish for one day the smaller the cheaper it will be get a old Styrofoam shipping box and cut it up to fill the inside of your box then put fish in bag add enough water to cover fish then add oxygen and double bag cover with news paper and if your in a cold climate add heat packs.If you do this before you ship it cuts down on time in box. I sent my mother fish from new york to Oklahoma over night in a 10 by 10 by 10 inches box It was like 95 bucks so the less water and the smaller the box the cheaper it is. You might want check out the post office next day delivery if it fits it ships. Hope I helped you out Noel