Answer: are
Explanation: The words or phrases connected by prepositions do not affect the verb. Therefore, the verb typically agrees with the subject preceding the preposition. This means if the subject before the preposition is plural, a plural verb is used and if it’s singular, a singular verb is used. However, if there are multiple prepositions with multiple subjects in the same sentence, the verb will agree with the first subject before the first preposition.

In this sentence, “of” is the preposition, and “the prices” is a plural subject. Since the sentence is in the present continuous tense, the correct answer is “are.”