Getting the parts from the dealer would be your most expensive option.
Your least expensive route would probably be to get the whole rear from a salvage yard.
Alternatively, you can get the parts from a mail-order place like Summit or Jegs. A ring and pinion package (with gears, seals, bearings, fluid, etc.) is around $300. As far as the other broken gears (I guess in the differential itself?), try
www.gearsrus.com (actually, you should try them for all of it).
Jim