Just to add, Archie is correct for the most part. Only I wouldn't bother with paying for the consumer reports report. (I did and there was nothing I didn't already find for free, and I actually found more info than they provided anyway).
I would hit the lexus forums (this one and carspace.com seem to be the better ones) to see what other people are getting them for.
Of course the forums are no substitute for actually having the real figures. There are a slew of free sites out there (google is your friend) that will tell you the real cost. edmunds.com and cars.com are good starts, but they pretty much only list the basic info. If you dig deeper, you'll find the holdback (edmunds mentions it actually), the wholesale holdback, the TDA, and of course the invoice price.
For a jump start (this is all from memory) for lexus, the holdback is 2% of base MSRP, the wholesale is another 1%, and I believe the TDA varies with models (this one is harder to dig up) but I think is around $400-$600.
Subtract all that from invoice and you'll have what the dealer really pays for the car.