priceless (adj.)

c. 1200, pris, "non-monetary value, worth; praise," later "recompense, prize, reward," also "sum or amount of money which a seller asks or obtains for goods in market" (mid-13c.), from Old French pris "price, value, wages, reward," also "honor, fame, praise, prize" (Modern French prix), from Late Latin precium, from Latin pretium "reward, prize, value, worth" (from PIE *pret-yo-, suffixed form of *pret-, extended form of root *per- (5) "to traffic in, to sell").

Praise, price, and prize began to diverge in Old French, with praise emerging in Middle English by early 14c. and prize, with the -z- spelling, evident by late 1500s. Having shed the extra Old French and Middle English senses, price again has the ancient sense of the Latin original. To set (or put) a price on someone, "offer a reward for capture" is from 1766.