If you take the maintenance costs out of it, it's roughly the same as driving, and a LOT quicker. The benefits increase the further you fly as well.
For instance, this weekend my mate is flying me and the bro-in-law down to Old Buckenham airfield in Norfolk, from RAF Leuchars, in a home-built Jabiru*. Fuel prices are same as car fuel, conservative flying (90-100mph ground speed) averages somewhere around 16L per hour, and it's about 3 hours each way, so we're looking at around 100L/£120 between the 3 of us to get there and back. Landing fees, sometimes free as my buddy is a nav on the Tornados. If not, it's about £30 at the smaller airfields.
Driving it would be an 860 mile round trip, and in a car averaging 35 mpg (I bloody wish!) that would be about 24.5 gallons = roughly £130 in petrol. Plus about 8 hours drive each way.
Having said that, he reckons maintenance and insurance can be a bugger.
*home-built means home-serviced = mucho cheapness compared to say a Cessna engineer coming out to service.