Cost all depends on weight, and destination.
When I ship I use only a small amount of water, just enough tp entirely cover the fish, but make sure there is enough air trapped in the bag. Oxygen is more important than water volume. I also use 48 hour heat packs during col d weather.
Most of my fish end up in boxes under 10lbs, and the cost to ship is between $50-$60 with USPS, depending on destination.
And as far as being late, most packages whether USPS or other shippers end up on the same planes, so if there is bad weather, all planes to that destination are late, so no company gives better service than another.
I always include a phone number on the box, with instructions to call the receiver upon arrival at the local post office.
And when I receive fish, I take the day off, and go pick them up myself when they arrive at the post office, saves them driving around in a hot, or cold truck all day.