Amount of money in diagram (6)
I believe the answer is:
figure
I believe this clue is a double definition.
'amount of money' is the first definition.
(figure is a kind of amount of money)
'diagram' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for figure that I've seen before include "The written symbol of a number" , "Diagram or digit" , "Shape; number" , "Statistic - physique" , "Number; statue" .)