The most common and most likely answer to this crossword clue is the 7 letter word COSTING
I've seen this crossword clue in The Daily Telegraph
C
O
S
T
I
N
G
Buddy explains!

The straight part
We know that "Estimating expenses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case estimating expenses = costing.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 COSTING mean?
COSTING verb- To incur a charge of; to require payment of a (specified) price.
- To cause something to be lost; to cause the expenditure or relinquishment of.
- To require to be borne or suffered; to cause.
- To calculate or estimate a price.
- The estimation of the cost of a process or product.
- To incur a charge of; to require payment of a (specified) price.
- To cause something to be lost; to cause the expenditure or relinquishment of.
- To require to be borne or suffered; to cause.
- To calculate or estimate a price.
- The estimation of the cost of a process or product.