If you say that something is costly, you mean that it costs a lot of money, often more than you would want to pay. 昂贵的
adjective [原级] 昂贵的，值钱的；造成严重损失的，代价大的
Having professionally made curtains can be costly, so why not make your own? 买专业制造的窗帘可能很贵，你为什么不自己做呢？
