The word "un-costly" means not expensive or not costing much. Its antonyms, on the other hand, are words that express the opposite meaning. Some antonyms for "un-costly" are costly, expensive, exorbitant, lavish, and pricey. Costly means something that is expensive or requires a significant amount of money. Expensive, exorbitant, and pricey are used if something is costly beyond what is reasonable. Lavish expresses something that is luxurious and sometimes wasteful. These words are often used in business or consumer contexts, where prices and expenses are significant factors in decision-making. Knowing and using these antonyms will help you communicate more precisely and effectively in your writing and conversations.