See a lot going for a song (5)
I believe the answer is:
cheap
'going for a song' is the definition.
(old-fashioned phrase meaning 'cheap')
'see a lot' is the wordplay.
'see' becomes 'C' (the word for the letter, according to Chambers).
'a lot' becomes 'heap' ('heap' can be a synonym of 'lot').
'c'+'heap'='CHEAP'
(Other definitions for cheap that I've seen before include "Tawdry - inexpensive" , "bargain" , "Contemptible" , "good value" , "Base" .)