Antonyms for "free of cost" include "expensive," "costly," "pricy," "high-priced," "pricey," "premium," "valuable," and "luxurious." These words indicate a significant expense or investment is required to acquire something. In a market economy, it is common to pay for goods and services. However, there are instances where free or low-cost provisions are available. In these scenarios, the opposite of free of cost would be "fee-based," "pay-per-use," or "subscription-based." Hence, the antonyms for "free of cost" vary based on the context of the situation. The words that indicate expenses are necessary to acquire something are commonly used in industries such as luxury brands, professional services, and specialized markets.