Find out exactly where the job site is. Given the growth rates and patterns, the "DC Metro Area" means anything from the WV Panhandle east to the Chesapeake Bay Bridge (and some would argue the eastern shore should be included), north to Baltimore, and south to Fredericksburg.
If you're working in Loudoun or Stafford then the cost of living, while growing quickly, isn't as high as areas closer to DC... which is why they're growing!
I'd recommend living in VA over MD or DC. WE have lower taxes, lower crime rates, better schools, and better gun laws.
FWIW I live in Sterling and work in Rosslyn, just across the Potomac from DC and Georgetown. I car-pool, leave the house at 6:30, and am at work at 7:15 in the mornings. Afternoon traffic is worse for some reason, and the commute can be over an hour. Of course, if there's an accident or the least bit of problem with the weather, that changes in a hurry...