Crossword Genius

Next felon last to thieve off an empty bus on offer (2,3,5)

Ross

I believe the answer is:

up for grabs

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

'next felon last' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'to thieve off an empty bus on offer' is the wordplay.
I cannot really understand how this works, but
'to' could be 'for' and 'for' is located in the answer.
'an' could be 'a' and 'a' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for up for grabs that I've seen before include "Available for anyone to claim" , "Ready for the taking" , "easily obtainable" .)

I've seen this clue in the Sydney Morning Herald.
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