I have stayed at the Hilton across from Downtown Disney on Buena Vista Dr numerous times for conferences. The rate available on Hotels.com, Expedia, or Travelocity is usually about the same as what I have paid at that hotel for a "convention" rate, which has usually been about $99/night.
From that hotel, you can walk over to Downtown Disney and catch the Disney bus to the park of your choice. That will keep you from paying the exorbitant parking rates at the Disney parking lots.