c.1200, pris "value, worth; praise," later "cost, recompense, prize" (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-, from root *per- (5) "to traffic in, to sell" (cf. Sanskrit aprata "without recompense, gratuitously;" Greek porne "prostitute," originally "bought, purchased," pernanai "to sell;" Lithuanian perku "I buy").
Praise, price, and prize began to diverge in Old French, with praise emerging in Middle English by early 14c. and prize being evident by late 1500s with the rise of the -z- spelling. Having shed the extra Old French and Middle English senses, the word now again has the base sense of the Latin original. To set (or put) a price on someone, "offer a reward for capture" is from 1766.