Island jewel upset heartless kids a lot (9)

I believe the answer is:

megabucks

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'a lot' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'island jewel upset heartless kids' is the wordplay.
'island' becomes 'cuba' (Cuba is an example).
'jewel' becomes 'gem' (synonyms).
'upset' is a reversal indicator.
'heartless' suggests removing the centre.
'kids' with its centre taken out is 'ks'.
'cuba'+'gem'='cubagem'
'cubagem' in reverse letter order is 'megabuc'.
'megabuc'+'ks'='MEGABUCKS'

Can you help me to learn more?

(Other definitions for megabucks that I've seen before include "A fortune!" , "Vast sums of money" , "Huge money" , "Many grand" , "large sum of money" .)

I've seen this clue in The Daily Express.

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