Ah, gotcha...it’s extremely, extremely expensive! (1,3)
I believe the answer is:
i see
'ah gotcha' is the definition.
(I've seen this in another clue)
'it's extremely extremely expensive' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'extremely' suggests removing the centre (only the extremes of the word are used).
'its' with its centre removed is 'is'.
'expensive' with its middle taken out is 'ee'.
'is'+'ee'='I SEE'
(Other definitions for i see that I've seen before include "Expression of dawning comprehension" , "So that's the way the cookie crumbles!" , "Got it now!" .)