A few years ago you could pickup complete PWS 433A/AU and PWS 500A/AU systems for less than $150 U.S. on eBay, and there were always half a dozen or more available at any given time. The PWS600A/AU's were a different story entirely, perhaps because they didn't sell as well as the other two Miata variants.
These days however, only one or two are ever listed and the price has gone through the roof.
Supply and demand I suppose.
International shipping would probably cost far more than the computer itself, depending on where it was going.
In a happy world, it will go to a loving home somewhere within easy driving distance from it's current home and the knowledge that it was going to be loved and used as it was intended would be payment enough.
In the real world however, you'll be lucky to get a few hundred dollars for the parts, and should you sell them eBay they will likely wind up in the lairs of the woebegotten obsolete computer parts warehouses. As much as we're all aware of the necessity of said lairs, it surely chafes to pay their premium when that one components made entirely of unobtanium can only be found in their treasure horde.