They should be sending you an empty box with a label on it to ship their company property back to them. Talk to whoever is responsible for ensuring they receive their equipment. That should not be paid by you but it is on them to eat those costs. Most companies will have that shipped as priority and pay extra, so it shouldn't take more than a few days to get back to them, even if they are overseas. Planes fly all day everyday across the world with packages.

It does not matter the cost of the machine. It is their property. Do not keep their property because that would make you a thief and you would be in the wrong. It is completely normal for a company to retrieve any outstanding property they have as they may have data on there which they own, not you. Make sure you clear out any of your personal files before sending it back but do not do anything that would jepardize your relationship with a reference.

Good luck.