Maybe charge writer in old case of sacrilege (7)
I believe the answer is:
expense
'maybe charge' is the definition.
(a charge is a kind of expense)
'writer in old case of sacrilege' is the wordplay.
'writer' becomes 'pen' (something which writes).
'in' means one lot of letters goes inside another.
'old' becomes 'ex' (prefix meaning former or onetime).
'case of' suggests removing the centre (outsides of).
'sacrilege' with its centre taken out is 'se'.
'ex'+'se'='exse'
'pen' placed inside 'exse' is 'EXPENSE'.
(Other definitions for expense that I've seen before include "Money spent in the course of work" , "Disbursement" , "damage" , "Outlay or cost" , "What something costs" .)