One antonym for the phrase "cost next to nothing" could be "cost a fortune." This phrase indicates that something is very expensive, and the opposite of its low-cost counterpart. Other antonyms for "cost next to nothing" might include "pricey," "costly," or "expensive." These words all convey a sense of significant expense, where the item or service in question is not affordable for everyone. Using antonyms can help to provide contrast in language and add specificity to your writing. By highlighting the opposite of "cost next to nothing," a writer can more effectively convey the importance of budgeting, saving, and making wise financial decisions.