The most appropriate antonym of the word "inexpensive" is:

Option 2: Valuable

Explanation: The word "inexpensive" means low in cost or not expensive. Its antonym should convey the opposite meaning, which would be something of high cost or expensive. Option 2, "valuable," fits this description as it means having great worth or being highly prized, which implies a higher cost or expense. Therefore, option 2 is the most appropriate antonym for "inexpensive" in this context.