Not much in clothes shop - changed into thong (4,2,7)
I believe the answer is:
next to nothing
'not much' is the definition.
('next to nothing' means almost nothing)
'clothes shop changed into thong' is the wordplay.
'clothes shop' becomes 'Next' (Next is a clothing shop).
'changed' indicates anagramming the letters.
'into'+'thong'='intothong'
'intothong' with letters rearranged gives 'tonothing'.
'next'+'tonothing'='NEXT TO NOTHING'
'in' acts as a link.
(Other definitions for next to nothing that I've seen before include "Not much" , "Lacking neighbours" , "utterly unimportant" , "Very little" .)