having a high price; "costly jewelry"; "high-priced merchandise"; "much too dear for my pocketbook"; "a pricey restaurant"
If you describe someone's action or mistake as costly, you mean that it results in a serious disadvantage for them, for example the loss of a large amount of money or the loss of their reputation. Psychometric tests can save organizations from grim and costly mistakes
If you say that something is costly, you mean that it costs a lot of money, often more than you would want to pay. Having professionally made curtains can be costly, so why not make your own? = expensive inexpensive