Sort of country where shopper goes on to spend extravagantly (9)
I believe the answer is:
bluegrass
'sort of country' is the definition.
(sort of country music)
'shopper goes on to spend extravagantly' is the wordplay.
'shopper' becomes 'grass' (I've seen this before).
'goes on' means one lot of letters go next to another.
'to spend extravagantly' becomes 'blue' (blue can mean to waste money).
'grass' put after 'blue' is 'BLUEGRASS'.
'where' is the link.
(Other definitions for bluegrass that I've seen before include "Kind of country music" , "Style of country music from Kentucky" , "Style of US country music" , "American hillbilly music" , "A type of country music" .)