A relative early breechloader, say 1870s-1880s.
Possibly 20 gauge.
The lever configuration is quite standard for the time:
turning the long bottom lever will tip the barrels to open the gun.
The smaller lever or key is holding the forend in place with the barrels. Turn it to disassemble the gun.
The high starting price may be due to the link to crown prince Rudolf, but I think this is doubtful....

fuhrmann