Best expenses cover parking (7)
I believe the answer is:
outplay
'best' is the definition.
'expenses cover parking' is the wordplay.
'expenses' becomes 'outlay'.
'cover' is an insertion indicator.
'parking' becomes 'p' (abbreviation on road signs).
'outlay' placed around 'p' is 'OUTPLAY'.
(Other definitions for outplay that I've seen before include "Act better" , "Defeat (sport)" , "Perform better than" , "As sportsperson, overcome" , "Get the better of" .)