Buying Advice - Looking at Cars

Does anyone have access to the auction pricing for 2008 and 2009 E60's with under 50k miles?

CPO I am seeing anywhere between $50k-$60 for 2009's and $45k-$50k for 2008's.

Non-CPO are not that much less. I am aware of good 3rd party warranties with a company like NAC, but what is an acceptable price for an M5 like this:

http://www.perillobmw.com/certified-...99C043025.aspx

Any advice on how to approach negotiations with dealers of CPO and Non-CPO cars based on the auction/trade in market? Any advice would be great. I am really close, I am going to test drive a local '07 with SMG that's for sale at a local Porsche dealer to see how I like the SMG. I am coming from a manual S4, so I don't expect any real issues.