Don't spend penny on brush (5)
I believe the answer is:
skimp
'don't spend' is the definition.
(to skimp is to avoid spending money)
'penny on brush' is the wordplay.
'penny' becomes 'p'.
'on' says to put letters next to each other.
'brush' becomes 'skim' (both can mean to touch or pass over lightly).
'p' put after 'skim' is 'SKIMP'.
(Other definitions for skimp that I've seen before include "Use less to economise" , "Cut back on resources" , "Withhold" , "Spend not enough time and care on (job)" , "Try to economise" .)