When it comes to billing and invoicing, businesses often use the term "justifiable charge" to denote a fee that is legitimate and reasonable based on the services provided. However, there are several other synonyms that can be used in place of this term. These include acceptable cost, reasonable fee, legitimate expense, fair charge, justified payment, and warranted expenditure. Each of these phrases conveys the same idea - that the fee being charged is justified and reasonable for the work that has been done. As such, businesses may choose to switch up their language to avoid repetition and provide clarity in their invoicing.