US pricing for he 2011 Infiniti M performance luxury sedan models which will go on sale across the nation starting from March have just been announced.
The 2011 Infiniti M56 price is just 350 USD above the previous generation, and under the bonnet customers will find the 5.6-litre V8 producing 420 HP which get send to the standard 7-speed automatic transmission.
The 2011 Infiniti M56 price starts at 57,900 USD and reaches 60,400 for the AWD version.
The 2011 Infiniti M37 price was also announced, and in this case power is provided by a 3.7-litre V6 that unleashes 330 HP through the same 7-speed automatic gearbox. The 2011 Infiniti M56 price starts at 46,500 USD, while the model featuring the automaker’s Intelligent All-Wheel-Drive system costs 48,650 USD.  
Infiniti press release :
Infiniti today announced an interim price increase on the 2011 Infiniti M
performance luxury sedan, which went on sale last March. The price
increase of $250 USD for M37 models and $350 USD for M56 models is
effective immediately.
About the 2011 Infiniti M
The all-new 2011 Infiniti M embraces the essence of all things Infiniti –
style, performance, luxury, craftsmanship and technology – taking each
to the highest levels ever for Infiniti’s halo sedan. It is available
in M37 and M56 model designations, with rear-wheel drive or Infiniti’s
Intelligent All-Wheel Drive system. The M37 features a 330-horsepower
3.7-liter V6 engine – with increased power and fuel economy versus the
previous generation M35’s 3.5-liter V6. The M56 also offers more power
and better fuel economy from an all-new 420-horsepower 5.6-liter V8
(versus the previous generation M45’s 4.5-liter V8). Both the M37 and
M56 engines feature Infiniti’s advanced VVEL (Variable Valve Event &
Lift) system and all models are equipped with a standard 7-speed
automatic transmission. A special Sport Package, offered on rear-wheel
drive models, features 4-Wheel Active Steer (4WAS), sport-tuned
suspension, Sport Brakes and 20-inch wheels and tires.
The 2011 M is also a showcase for Infiniti’s advanced, user-focused
technologies, carrying on the tradition of the previous generation M.
New technologies include Infiniti Drive Mode Selector, Active Noise
Control, Blind Spot Warning (BSW), Blind Spot Intervention™ (BSI),
Forest Air™ system, Eco Pedal and Active Trace Control. The 2011 M also
offers a next-generation Infiniti Hard Drive Navigation System, Bose®
Studio Surround® premium audio system, Intelligent Cruise Control
(Full-Speed Range), Lane Departure Warning (LDW) and Lane Departure
Prevention (LDP) systems, Distance Control Assist (DCA), Intelligent
Brake Assist (IBA) with Forward Collision Warning (FCW) and Front
Pre-Crash Seat Belts.
The new Manufacturer’s Suggested Retail Prices (MSRP)* are:

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Model Engine/Transmission MSRP
Infiniti M37 3.7-liter V6 / 7-speed automatic $46,500 USD
Infiniti M37x AWD 3.7-liter V6 / 7-speed automatic $48,650 USD
Infiniti M56 5.6-liter V8 / 7-speed automatic $57,900 USD
Infiniti M65x AWD 5.6-liter V8 / 7-speed automatic $60,400 USD

The M’s dramatic sports styling provides a coefficient of drag of just
0.27 Cd, while the roomy, comfortable interior environment features
standard leather-appointed seating, standard Japanese Ash wood trim or
available silver powdered genuine White Ash wood trim and available
premium audio and climate control systems. Key standard features
include Infiniti Intelligent Key with Push Button Ignition, XM®
Satellite Radio (XM® subscription required, sold separately), Bluetooth®
Hands-free Phone System and power-sliding glass tinted moonroof.

Source: Infiniti