Short trousers could be a real bargain (5)
I believe the answer is:
steal
'bargain' is the definition.
('steal' can be a synonym of 'bargain')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for steal that I've seen before include "Pilfer" , "Lift - pocket" , "Walk off with" , "bargain?" , "Take unlawfully" .)