I did a quick check at edmunds and without the floormats, edmunds says the average price paid for that car in the Boston area is $42,900.
I would try for around $42k. I'm not sure what kind of lease payment that translates into. My car is $37,225 MSRP. I don't remember the exact buy price as our contract only quoted my lease rate, but it is something in the low-to-mid 33s. And I do not qualify for the $500 loyalty cash, only the $750 incentive. So if I could get $3500+ off on a car with less of a markup, you should be able to do at least $4k off just by adding the $500 loyalty cash, without even taking into account the higher markup provided by all the additional options on your car.
I understand what you mean as far as having a lower payment. I used to pay $690/month on an X5. But times change and in this economy I was forced to cut my budget. At least I can still drive a BMW.