Source : Webster's Revised Unabridged Dictionary (1913)

Exorbitantly \Ex*or"bi*tant*ly\, adv.
   In an exorbitant, excessive, or irregular manner; enormously.

Source : WordNet®

exorbitantly
     adv : to an exorbitant degree; "prices are exorbitantly high in
           the capital" [syn: {extortionately}, {usuriously}]