The most common and most likely answer to this crossword clue is the 8 letter word EXPENSES
I've seen this crossword clue in Independent
E
X
P
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More clues leading to the result EXPENSES
Buddy explains!

The straight part
We know that "costs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case costs = expenses.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EXPENSES mean?
EXPENSES noun- A spending or consuming, often a disbursement of funds.
- The elimination or consumption of something, sometimes with the notion of loss or damage to the thing eliminated.
- Loss.
- To charge a cost against an expense account; to bill something to the company for which one works.