We found one dictionary that defines the word costlily:

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1. costlily: Wiktionary

Definitions from Wiktionary (costlily) ▸ adverb:  In a costly manner. ▸ Words similar to costlily ▸ Usage examples for costlily ▸ Idioms related to costlily ▸ Wikipedia articles (New!) ▸ Words that often appear near costlily ▸ Rhymes of costlily ▸ Invented words related to costlily