Amount spent to put firm on street (4)
I believe the answer is:
cost
'amount spent' is the definition.
(I've seen this in another clue)
'firm on street' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'street' becomes 'st' (abbreviation).
'co'+'st'='COST'
'to put' acts as a link.
(Other definitions for cost that I've seen before include "Amount to pay" , "Estimate the expense of doing" , "Suffering" , "estimate price" , "Amount required as payment" .)