Money spent on proscribed amateur (6)
I believe the answer is:
outlay
'money spent' is the definition.
(outlay can mean expenses)
'on proscribed amateur' is the wordplay.
'on' says to put letters next to each other.
'proscribed' becomes 'out' (synonyms).
'amateur' becomes 'lay' (similar in meaning).
'out' put next to 'lay' is 'OUTLAY'.
(Other definitions for outlay that I've seen before include "Money expended" , "Amount spent on something" , "cost" , "Initial expense" , "What it costs" .)