Even Shylock didn't demand this extravagant payment (2,3,3,1,3)
I believe the answer is:
an arm and a leg
'extravagant payment' is the definition.
(as in paying an arm and a leg for something)
I can't explain the rest of the clue.
(Other definitions for an arm and a leg that I've seen before include "a large amount of money" , "A lot" , "Two members" .)