If you don't ship a lot, it is pretty expensive. If using FedEx, it is cheaper to do hold at location. Just make sure it is a FedEx staffed office, and not a FedEx/Kinko place. Same goes for UPS. They can hold it at a hub. Safer on the coral/fish, and cheaper. If you plan on shipping more, it's better to pay the fee to have an account with them. You get a discount on shipping for having the account. If you ship a lot, the percent off gets bigger. USPS is unreliable in some areas. Even though it says overnight, doesn't mean that it goes everywhere overnight.
To save money, use less water. Unless you are shipping a colony, you don't need a large bag filled with water. The less weight, the cheaper. Unless the box is big. Then the weight doesn't matter, it goes by dimensional weight. If the actual weight is more then dimensional, you'll pay the actual. Hopefully that helps. I normally ship in either a 12X9X6, or a 12X9X9 box. Way cheaper for those boxes.