I have a local business that ships through everyone (USPS, UPS, FedEX, and Spee Dee). They check the rates for me, and see who can give me the best deal. Last time I had to ship a saddle, it only cost me $40. They also supply shipping material (and will package things for me) when it need it. I had my own box this last time.
Prior time before that, I used FedEx and it cost me over $100.
So if you have a shipping company that uses multiple companies, that’s your best bet for the best rate.
Certainly, put the saddle in the smallest box you possibly can. The bigger the box gets, the more expensive the shipping gets. Of course, make sure you get insurance and understand the terms of the insurance. Put the saddle in the box UPSIDE DOWN, fold the fenders in. It’s a good idea to wrap your saddle horn so it doesn’t get scuffed, and then of course wrap the saddle in protective material (as shipping companies usually aren’t gentle on things).