pretium

Pretium, pretii is second declension neuter. Price is expressed in the ablative - pretio parvo emere, magno pretio vendere - and that ablative of price is one of the standard uses worth learning as a phrase rather than a rule. The fixed idiom operae pretium est, "it is worth the effort", is common enough to be treated as a unit.

The corpus being what it is, the theological sense turns up constantly: pretium is the ransom, the price paid for redemption, and pretiosus is "precious" in the literal sense of costly before it is a compliment. Note that pretium is the price asked, while merces is the wage paid and praemium the prize won; they are not interchangeable. It gives French prix, Spanish precio, Italian prezzo, and English price, prize, praise and appreciate.