First, I negotiated my 2013 RX350 with Nav, Comfort, Premium and 19" rims from $49.9 down to $44.5 first. I did this via email negotiating with three dealers - two of which met my price. I knew I could get around 10% off sticker by checking forums, true car, etc.
Second, I checked on Edmunds forums to see the current lease factor and residual for a 36 month/12k lease and went to the dealer. You definitely need to know these numbers before going, I also downloaded a lease calculator app on my iPhone. I caught a big error from the finance manager who was using the wrong lease factor - my numbers were coming in $60 per month lower. I challenged him and he corrected it. The final was .001 MF and 60% residual, with cap cost of $2715 my monthly is $435
Unless you break these two apart - negotiated price and lease details - there is no way of knowing if you are getting a good deal.