Read pitch badly, when going for a song (4,5)
I believe the answer is:
dirt cheap
'going for a song' is the definition.
('going for a song' means sold cheaply)
'read pitch badly' is the wordplay.
'badly' indicates an anagram.
'read'+'pitch'='readpitch'
'readpitch' with letters rearranged gives 'DIRT-CHEAP'.
'when' is the link.
(Other definitions for dirt cheap that I've seen before include "rock-bottom prices" , "next to nothing" , "Extremely inexpensive" , "Greatly reduced in price" , "Ridiculously inexpensive" .)