First of chords, large number -- for a song! (5)

I believe the answer is:

cheap

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'for a song' is the definition.
(I've seen this in another clue)

'first of chords large number' is the wordplay.
'first of chords' becomes 'c' (hst letter of 'chords').
'large number' becomes 'heap' (I can't explain this - if you can you should believe this answer much more).
'c'+'heap'='CHEAP'

Can you help me to learn more?

(Other definitions for cheap that I've seen before include "Budget -cheesy" , "Tawdry - inexpensive" , "good value" , "Inexpensive or tasteless" , "Contemptible" .)

I've seen this clue in The Telegraph.

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