Around here (Princeton, NJ) a 'B' service costs around $280...and you don't get much for that amount. Basically an oil change and climate control filter (like the 'A' service) and also new windshield wiper inserts, tire rotation and some visual inspections. You could probably buy it a la carte for about $100. Fortunately, my dealer does not insist on the 'A' and 'B' systems and does regular oil changes instead for about $60. I buy the rest when it's needed.
Save your money. It's a rip off.