This is the 520th most frequent Japanese word.
費
Cost; expense.
費 is used within '費用' to refer to expenses or costs associated with an activity, here travel.
旅行の費用が高いです。
The travel expenses are expensive.
費 is used in '準備費' to indicate costs specifically allocated for preparation activities, in this case for a wedding ceremony.
結婚式の準備費を計算しました。
I calculated the wedding preparation costs.
費 is used in '費' of '月額費' to refer to fees that are periodic, specified here monthly for a service.