Price of firm’s time (4)
I believe the answer is:
cost
'price' is the definition.
('cost' can be a synonym of 'price')
'firm's time' is the wordplay.
'firm's' becomes 'cos' (a firm is a company).
'time' becomes 't'.
'cos'+'t'='COST'
'of' is the link.
(Other definitions for cost that I've seen before include "Come to" , "Outlay required to buy" , "Total spent for goods or services" , "Amount required as payment" , "Charge" .)