Synonyms for the term "costful" can be used to replace this word while retaining its primary meaning of being expensive or having a high cost. Some alternative words that can be employed include pricey, costly, valuable, high-priced, extravagant, premium, dear, rich, luxuriant, and lavish. These synonyms are apt for describing items or services that are not economical or require a substantial sum of money for acquisition. It is important to consider the context when selecting the word that best fits the intended message, ensuring accurate and effective communication when discussing expensive or high-cost matters.