At last! the Yarra banker's attention (3)
I believe the answer is:
ear
'attention' is the definition.
(having someone's ear is having their attention)
'at last the yarra banker's' is the wordplay.
'at last' suggests the final letters.
The final letters of 'the yarra banker' are 'EAR'.
(Other definitions for ear that I've seen before include "Appreciation of sounds" , "That makes sense" , "Listening organ" , "Van Gogh missing body part" , "Listener in the cornfield" .)