The priciest items on the menu were the Filet Mignon and the Lobster Thermidor. The priciest gift I've ever received was a diamond necklace from my grandmother. The priciest perfume I've ever owned was a bottle of Chanel No. 5.
Colloquialism
She made the priciest mistake of her life by investing in a Ponzi scheme.
Informal usage
The car we bought was the priciest thing we've ever purchased.
Metaphorical usage
The tour of the Eiffel Tower was the priciest adventure we've been on, in every sense of the word.
Idiomatic usage
Driving a luxury car is the priciest aspect of being a celebrity.
Something that is priceless is extremely valuable and worth more than any amount of money. It is a highly valuable and irreplaceable asset, treasure, or skill.