The phrase "astronomical prices" means that something is extremely expensive, like the high prices you might associate with the vastness of the universe. Full definition
There are a relatively small number of iconic rail journeys on the planet but they usually have astronomical price tags that put them out of reach of many. (flightstofancy.com)
Original copies go for astronomical prices; this one here is just a replica. (thatvideogameblog.com)
His works are displayed in the biggest contemporary art museums around the world and reach astronomical prices of more than ten million dollars in auctions. (polin.pl)