Mean man conserving energy (5)
I believe the answer is:
cheap
'mean' is the definition.
(I've seen this before)
'man conserving energy' is the wordplay.
'man' becomes 'chap' (I've seen this in other clues**).
'conserving' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mch).
'chap' placed around 'e' is 'CHEAP'.
(Other definitions for cheap that I've seen before include "bargain" , "Budget -cheesy" , "Inexpensive or tastelessy showy" , "Vulgar" , "Of very poor quality" .)