Cost of pair in charge of back entry (5,3)
I believe the answer is:
price tag
'cost' is the definition.
(I've seen this in another clue)
'pair in charge of back entry' is the wordplay.
'pair' becomes 'pr' (abbreviation).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'of back' shows that the letters should be reversed in order (I've seen 'back' mean this).
'entry' becomes 'gate' (I've seen this in another clue).
'gate' backwards is 'etag'.
'pr'+'ic'+'etag'='PRICE TAG'
'of' is the link.
(Other definitions for price tag that I've seen before include "Label showing cost" , "Amount to be paid" , "Label indicating cost" , "Cost of a project, perhaps" , "shows outlay required" .)