I used to live in Arlington. the housing is a little crazy but you need to look at the bigger picture:
1. You will not need a vehicle, so sell it. You will also no longer need auto insurance so there is another expense you no longer need.
2. Ask your employer for a reimbursement package for the Metro. If you're living on the south side of Arlington at the Pentagon/Pentagon City/Crystal City stops and heading to Capitol South then the company should reimburse you roughly $75/month for transportation to and from work. There's another expense.
3. Everything is really close in DC. I like to tell people I learned to walk twice in my life: Once when I was a baby, and once when I moved to DC.
You'll find yourself walking everywhere and your perception of space and something being "far away" will change drastically. Cabs are for suckers, unless you're heading to Adams Morgan at night, or you find yourself in Anacostia at 3 a.m. after falling asleep on the Greenline Metro after a night on U-Street.
4. If you work on the Hill, get VERY ACQUAINTED with the Interns, Staff Assistants, and Schedulers. They know of all the receptions offering free food and drinks. Newbies to DC have survived on finger food and free beer for generations...this will not change!
5. If you don't work on the Hill, there is NO excuse to be more than 2 degrees of separation from one of the above referenced interns, staff assistants, or schedulers. DC is a networking city. There might be a few million people there, but you're just a handshake and a slip of the tongue away from being front page news. USE CAUTION WHEN PRACTICING YOUR FIRST AMENDMENT RIGHT, remember that reporters have that right as well!
Hope this helps.
Your best bet is to do a craigslist apartment search and interview for an apartment. I know it sounds crazy but everyone who just moves there has 5 other roommates for a 3 bedroom/2 bath house. That's just the way it works.