Be frugal with millions found in waste container (5)
I believe the answer is:
skimp
'be frugal' is the definition.
(to skimp is to be frugal or economical)
'millions found in waste container' is the wordplay.
'millions' becomes 'm' (abbreviation).
'found in' indicates putting letters inside.
'waste container' becomes 'skip' (container for waste from a building site).
'm' going into 'skip' is 'SKIMP'.
'with' is the link.
(Other definitions for skimp that I've seen before include "Limit in quality or quantity" , "Stint in order to economise" , "Work hastily" , "Cut corners" , "Use minimal amount" .)