The Collaborative International Dictionary of English v.0.48:

Extortionate \Ex*tor"tion*ate\, a.
   Characterized by extortion; oppressive; hard.
   [1913 Webster]

WordNet (r) 3.0 (2006):

extortionate
    adj 1: greatly exceeding bounds of reason or moderation;
           "exorbitant rent"; "extortionate prices"; "spends an
           outrageous amount on entertainment"; "usurious interest
           rate"; "unconscionable spending" [syn: exorbitant,
           extortionate, outrageous, steep, unconscionable,
           usurious]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "extortionate":
   all-devouring, all-engulfing, arousing, bloodsucking, clamant,
   clamorous, crying, cutthroat, demanding, draining, educible,
   eductive, elicitory, eradicative, evocative, exacting, exactive,
   excessive, exigent, exorbitant, extortionary, extortive,
   extractive, extravagant, fancy, gouging, grabby, grasping,
   grossly overpriced, immoderate, importunate, inflationary,
   inordinate, insistent, instant, loud, lupine, out of bounds,
   out of sight, outrageous, overpriced, parasitic, persistent,
   pertinacious, predacious, predatory, preposterous, pressing,
   prohibitive, rapacious, raptorial, ravening, ravenous, sharkish,
   skyrocketing, spiraling, taxing, unconscionable, undue,
   unreasonable, unwarranted, uprooting, urgent, usurious, vulturine,
   vulturous, wolfish