$29 for car & driver + $9 each passenger.... so $38 for a climbing team of 2!
Also, the road doesn't open until 7:30 am... sometimes later: http://mtwashingtonautoroad.com/hours-dates-of-operation
That said using the Auto Road allows for some sweet linkups or a "quick" alpine climb if you have other agendas. The hiking approach from PNVC to the climbing for me usually takes a bit over 2 hours (slower parties have reported 3 hours, really fit teams can probably run it in just over an hour).
The real time saver is being able to get back to the car 30 minutes after the pitched climbing ends (vrs. 1.5 hours if you hustle down Lion's Head Trail).
A real disclaimer is needed here regarding weather.
DO NOT use the auto road approach if there is a chance of afternoon thunderstorms/poor weather. You do not want to "retreat up" in poor weather, and the rock pile sees a lot of iffy weather. Pick a nice high pressure day for this tactic!
I haven't done a link up near this size yet but I did do a Pinnacle/Salt Packed/Eaglet day years ago that was pretty fun.