The only time I shipped a saddle, I shipped through FedEx Ground and it was ~$65. (English saddle in a box that was a bit large for it, but that's the box it came in & I didn't want to try and buy another box for it) At first I brought it to a FedEx location (one of the ones in the office store) and they quoted me something crazy like the quote you got, but when I went through their website it was much lower. Not sure if the person behind the counter didn't know what they were doing or what.
Definitely put it into the smallest box you can without risking damaging it. If in doubt, pack it up and bring it to the post office, UPS Store, or wherever and have them help you out. They ship a lot of things and would probably know what's going on. Try to avoid the office store locations- they don't seem to get as much training/experience shipping unusually big or heavy things.