Just right for the single - and a bargain (5)
I believe the answer is:
ideal
'just right' is the definition.
(thesaurus)
'the single and a bargain' is the wordplay.
'the single' becomes 'i' (one).
'and' says to put letters next to each other.
'a bargain' becomes 'deal' ('deal' can be a synonym of 'bargain').
'i'+'deal'='IDEAL'
'for' acts as a link.
(Other definitions for ideal that I've seen before include "Nonpareil" , "without flaws" , "Coal-mining waste" , "In her dreams" , "Pattern" .)