Yes, you should very much expect to pay at, near or slightly below invoice now for an in-stock 2009, even though it's a Lexus.
That said, take a good hard look at some of the options before buying the base model. To me, the base model is entirely unsatisfying, and doesn't have a great luxury feel. The option packages are not particularly expensive either, as far as luxury car option packages go.
Even if you just get the minimal "premium package" - that only adds $400. For that, you get the perforated leather (looks much better I think), air conditioned seats (who wouldn't want that?) and real maple trim, vice plastic. Incredibly worth it.
By itself, the IS 250 is a nice car. To truly be worthy of a Lexus though, I think you probably need a few options, at least some basic ones. I bought mine used (5K miles on it), with the options you see below.
Good luck!