noun which may take the genitive case particle 'no'
priceless; invaluable
Used to describe something of such great value that it cannot be measured in money. Often appears in set phrases like 値千金の～.
彼の助言は値千金の価値があった。
His advice was worth its weight in gold.
この一枚の写真は我が家にとって値千金の宝物だ。
This single photograph is a priceless treasure for our family.
貴重 means 'precious' or 'valuable' in a more general sense, while 値千金 emphasizes that something is so valuable it cannot be priced.
Compound of 値 (value) and 千金 (a thousand pieces of gold), literally 'worth a thousand gold'. The exact historical derivation is uncertain, but the expression is conventionally associated with something of immeasurable worth.