It's hard to quote a price if you don't specify how you would spec the car, but at full MSRP with the Exec Package and the 20' wheels, your payment would be around $1,690. Subtract about $30 for every $1k you can negotiate off of MSRP. This will get you in the ballpark +/- a few bucks.
Current: 2013 Monte Carlo Blue F10 M5 (ED on 9/1/12)
Previous: 2009 Carbon Black E60 M5, 2006 Silverstone II E60 M5, 2003 Sterling Grey E39 M5, 2000 Anthracite E39 540i6, 1998 Jeep Grand Cherokee 5.9 Limited, 1990 Eagle Talon TSi AWD, 1978 Mazda RX-7