Crossword Genius

Involving muck but little brass? (4,5)

Ross

I believe the answer is:

dirt cheap

I'm a little stuck... Click here to teach me more about this clue!

'involving muck but little brass?' is the definition.
I can't judge whether this definition defines the answer.

'muck but little brass?' is the wordplay.
'muck' becomes 'dirt' (I've seen this before).
'but little brass?' becomes 'cheap' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'dirt'+'cheap'='DIRT-CHEAP'

Can you help me to learn more?

(Other definitions for dirt cheap that I've seen before include "Greatly reduced in price" , "rock-bottom prices" , "for very little money" , "doing little damage?" , "Going for a song" .)

I've seen this clue in The Independent.
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