Excessive tax? Not to Eire, surprisingly (12)
I believe the answer is:
extortionate
'excessive' is the definition.
(thesaurus)
'tax? not to eire surprisingly' is the wordplay.
'surprisingly' indicates an anagram.
'tax'+'not'+'to'+'eire'='taxnottoeire'
'taxnottoeire' anagrammed gives 'EXTORTIONATE'.
(Other definitions for extortionate that I've seen before include "Outrageous" , "Grasping" , "Overly demanding" , "Preposterous" , "(Of a price) much too high" .)