Difficult at college being short of money (4,2)
I believe the answer is:
hard up
'short of money' is the definition.
'difficult at college' is the wordplay.
'difficult' becomes 'hard' ('hard' can be a synonym of 'difficult').
'at college' becomes 'up'.
'hard'+'up'='HARD-UP'
'being' is the link.
(Other definitions for hard up that I've seen before include "Badly-off" , "Panto Baron; needy" , "Poor" , "Struggling with budget" , "Impecunious" .)