Rent by oneself for much less (3,5)
I believe the answer is:
let alone
'much less' is the definition.
(I've seen this before)
'rent by oneself' is the wordplay.
'rent' becomes 'let' (I've seen this in another clue).
'by oneself' becomes 'alone' (being by oneself is being alone).
'let'+'alone'='LET-ALONE'
'for' acts as a link.
(Other definitions for let alone that I've seen before include "Don't touch" , "Not to mention (thing)" , "Not to mention - much less - avoid" , "Not to mention, never mind" , "Don't bother someone - allow to be solitary" .)