The most common and most likely answer to this crossword clue is the 4 letter word RIAL
I've seen this crossword clue in The Daily Telegraph
R
I
A
L
More clues leading to the result RIAL
Buddy explains!

The straight part
We know that "Bit of money" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bit of money = rial.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 RIAL mean?
RIAL noun- The official currencies of Iran, Oman, and Yemen.
- An old gold coin of England.