extortionate
adjective /ɪkˈstɔːʃənət/
  /ɪkˈstɔːrʃənət/
(rather informal, disapproving)- (of prices, etc.) much too high synonym excessive, outrageous
- They are offering loans at extortionate rates of interest.
 - The prices they charge are extortionate.
 
Oxford Collocations DictionaryExtortionate is used with these nouns:- rate