If "costly" refers to price:
* Expensive: This is a more neutral term than "costly".
* Premium: This implies high quality and value.
* High-end: This suggests exclusivity and luxury.
* Investment: This emphasizes the long-term value of the purchase.
If "costly" refers to effort or time:
* Challenging: This implies a sense of accomplishment once the task is completed.
* Intricate: This emphasizes the complexity and beauty of the effort.
* Intensive: This suggests a high level of dedication and focus.
* Worthwhile: This emphasizes the value of the effort.
If "costly" refers to negative consequences:
* Risky: This implies potential for both positive and negative outcomes.
* Difficult: This focuses on the challenges involved.
* Complex: This emphasizes the intricate nature of the situation.
To help me give you the best word, please provide the sentence you are working with!