Find a big box, wrap the saddle in bubble wrap (can get from local PO) and I bought a couple of cheap sponges to position on the pommel and cantle aswell. Then stuff the box with newspapper and seal up with strong tape. I think it costs between £10 and £20 depending on size and weight of saddle to post wth Royal Mail.
Mizzy - if you go to royal mail website they have a service where they will pick up large parcels for you for a small charge. That is how I sent 2x heavyweight winter turnout rugs.,