I've shipped dozens. Go to Home Depot, and grab one of their moving boxes...even the largest one is under $2. Then put the saddle in, and pad it. Usually, I have enough packing peanuts/air bubbles around from my own packages that I just reuse those....when that's not an option, I just crumple up newspaper, although I usually wrap the saddle in a garbage bag first to prevent any ink transfer.
My most expensive saddle ever to ship was a 40lb western saddle that went from MA to CA, and it cost me $48. Dressage saddles are usually around $30, and I can get a little close contact anywhere it needs to go for under $20. I get insurance on all my saddles of course, but have never had an issue.
I ship all mine USPS.
Edit to add: While it may seem great to get a huge box so that you can stuff all sorts of padding in there, it's best to get the smallest box possible. It keeps the saddle tight and from shifting around too much. Also, the post office charges $$$$ for "oversized" boxes.
Also, to keep the size down, I usually curl the flaps into the gullet of the saddle. They pop right back out when it's taken out of the box.
I sold an English saddle and need to ship it. Would love some tips on packaging the saddle to send it in the safest way possible.
When I was trying saddles there were a few things that people did that stood out to me. The tack places made sure the box was big enough so that you can put in those air bags all around the saddle. Some pro boxing places will double box the saddle. All the saddles I received were shipped in boxes shaped so that the saddle was resting on its pommel on the bottom of the box.
Depending on the $$ involved, I would consider taking it to a pro box place and let them box and ship. Also make sure you insure it.
Make sure it's wrapped. I just got a nice (older) Passier jumping saddle that I purchased off of eBay. The seller had stuffed it in a box that was slightly too small and it's pretty scuffed up from the experience.
Get a box as close to 12 by 12 by 24 as possible. I have used larger boxes and cut them down and taped them up. You don't want the saddle to have any wiggle room. Put a piece of bubble wrap, maybe 12" by 30", over the top of the saddle and make sure the cantle and pommel are protected. Put the saddle in a plastic bag so no scuffing. Place it in the box upside down and gently roll the flaps inward so the fit snug in the box.
I used a moving box from Lowes Home Improvement, and raided the shredding bin at work for packing material. I put the saddle in a garbage bag, then filled in the voids with the shredded paper. The buyer emailed me when she got it and said it was in great shape upon arrival. I shipped it USPS with insurance and delivery confirmation for around $30, from NC to MO.