I recently replaced the right rear wheel bearing - part cost $136.67 from the service center. You probably could get for cheaper.
But other than that, you might want to look into the lower control arms - I have had some squeaking, and they too can cause that. But get a second opinion on this one, cause this is an expensive affair. I just got this done on my car, which has almost 140K on it. Both the lower front control arms with labor cost me $1500. Thats a lot - although you can get the two together on ebay for about $800.
Look up Carson Toyota and do some searching on ClubLexus.com. There is much more useful information over there in regards to anything. I got a pair of brand new Toyota Supra control arms for a hair over $500, about $250 each. And they are a wonderful upgrade to the oem SC control arms, it helps with the steering response quite a bit. I installed them myself so it only ran me the cost of parts total.
But to me, it really sounds more like the wheel bearing since even when my lower control arms were shot, it didn't make any kind of noise other than the thunk it makes when going from reverse to forward.