I have bought 2 Marathon Plus tyres online.
One of them came expertly folded and secured inside a box with other stuff, so only about as big as a large dinner plate. The tyre bead on that one has served me well for thousands of k's thus far.
The other one was unfolded, and gaffer-taped to the outside of the box holding my other stuff. That got some attention at the local post office.
Can't remember where I got them from, but I'm pretty sure it was less than 50% of what the local shops were/are charging.