But, by and large, the editors have chosen their biographers well: the most priceless source to be cited at the end of an essay is "personal knowledge" or "private information".
The Galápagos Islands were the source of Charles Darwin's theory of evolution and are seen as a priceless "living laboratory" for scientists.
The exchange is priceless and well worth the two minutes of your life to hear little Seth explain the source of the word "wii".
Through the efforts of book collectors, basic sources of history and priceless monuments of art and literature have survived that might otherwise have been irretrievably lost.
The recipe is one of the priceless peripheral details of this memoir.
It could be a priceless spec of gold, unnoticed.
Robson-Kanu's effort had the priceless element of surprise.
It's like a priceless work of art".
Soon, the building will be full of priceless works of art.
BBC News was salivating to attack itself: a remarkable sign of the priceless singularity of the BBC.
