Start of concert by that fellow on a piano, going for a song (5)
I believe the answer is:
cheap
'going for a song' is the definition.
(old-fashioned phrase meaning 'cheap')
'start of concert by that fellow on a piano' is the wordplay.
'start of' indicates taking the first letters.
'by' means one lot of letters go next to another.
'that fellow' becomes 'he' ('he' refers to a man).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'piano' becomes 'p' (musical abbreviation).
The initial letter of 'concert' is 'c'.
'c'+'he'+'a'+'p'='CHEAP'
(Other definitions for cheap that I've seen before include "Contemptible" , "Of very poor quality" , "Vulgar" , "Mean" , "Tawdry - inexpensive" .)