There are a number of comparsons of the IS250, G35, A4 and 335i.  How do they compare on pricing?  The following was taken from the Audi, BMW and Infiniti USA websites, trying to build those cars with the most expensive dealer offerings available from the build your own car feature.

IS250AWD
2.5-liter V6, four cam, four valves per cylinder, with dual Variable Valve Timing
204 hp @ 6,400, 185 lb-ft torque @ 4,800 rpm
Base MSRP.........................................$34,485.00
Additional Options...............................$6,656.00
-Voice-activated DVD Navigation System
-Luxury Package
-Premium package
-XM® Satellite Radio
-Rear spoiler
-Preferred accessory package
(includes cargo net, trunk mat
and wheel locks)
Delivery, Processing & Handling Fee.....$765.00
Total MSRP..............................$41,906.00

2008 Infiniti G35x AWD
3.5-liter (3,498cc) V6, double overhead cam, 4 valves per cylinder
306 hp @ 6,800 rpm, 268 lb-ft @ 4,800 rpm
Base MSRP........................$34,750.00
Technology Package...........$1,100.00
Premium Package...............$2,300.00
Rear Spoiler......................$550.00
Sport Package AWD............$1,100.00
Navigation Package............ $2,150.00
Splash Guards ...................$155.00
Trunk Cargo Net.................$60.00
Configured MSRP................$42,165.00
Destination and Handling.....$765.00
Total MSRP..................$42,930.00

Audi A4
3.123 L quattro 255 HP tiptronic
255 hp @ 6,500 rpm, 243 lb-ft @ 3,250 rpm
Base MSRP...............................$38,400.00
Exterior Dolphin.......................$750.00
Gray Metallic   
AM/FM/SAT* audio package.......$1,000.00
Audi acoustic parking system......$350.00   
Audi navigation system plus.......$2,100.00
with six disc CD changer*   
Cold weather package...............$550.00
Convenience package................$1,700.00
Power rear sunshade and...........$400.00
manual rear side door sunshades   
Preparation for mobile...............$500.00
phone (Bluetooth®)   
Rear side airbags......................$350.00
S line package..........................$900.00
Titanium package......................$500.00
Volterra premium leather...........$1,000.00
upholstery   
Total MSRP...........................$48,500.00

335xi Sedan
3.0-liter dual overhead cam (DOHC), 24-valve inline turbocharged
300hp 6-cylinder engine with twin-turbo technology
Base MSRP........................$41,200
Black Sapphire Metallic.......$550
Cold Weather Package........$850
Premium Package...............$2,650
Sport Package....................$1,000                 
Sports leather steering........$100
wheel with paddle shifters   
STEPTRONIC automatic.......$1,325
transmission   
Active Cruise Control..........$2,400
Comfort Access system.......$500
Navigation system..............$2,100
Rear manual side window....$575
shades with power
rear window shade   
HD radio...........................$350
iPod and USB adapter.........$400
Satellite radio with.............$595
1 year subscription   
Park Distance....................$350
Control (rear only)   
Destination & Handling:......$775
Total MSRP....................$55,720

The omission has been corrected.  The priced IS250 has a V6.

$2400 for the 335i active cruise control - nothing else included?  How active is that?  Does it work on stop and go traffic jams, like the one on the FX50?  On the new FX the car can go to a complete stop and then back again up to the preset distance.  THAT is cool.  How the BMW system works?

That's steep.  I'd gladly pass on that, though.

Well, actually I think it works quite well on my FX - the M has only the regular, fixed speed one.  No complains, unless the fact that it does not let me get close enough to the car in front as I wish.  I'd also like for it to start on the closest setting, if one wants it to.  I don't know about accuracy though.