I agree with the person who said to go with Priceline. Nothing in SB is cheap.Cheapest I know of is about 10 miles south, the motel 6 in Carpinteria.
Check with UC Santa Barbara for student housing to rent by the nights as Santa Barbara is very expensive to get a motel. You can try a nearby town like Goleta to the north or Carpenteria to the south.
RoomSaver.com travel saver guides have Santa Barbara hotels from $69-95. That might be the cheapest you could find. Check online prices or pick up a guide to get the discounts.
Use Priceline