If you want to live on the metro line, you should expect rent/mortage to be more expensive. We rent right now and the price went up at least $300 a month just for that convenience.
I don't know where you're going to work in Arlington, but if it's Federal Government, one of the perks is that the gov't will give you a stipend towards public transportation if you choose, that can offset some of the cost of the increased housing expense. Just food for thought. Other private sector jobs do offer something similar to this, but I can't speak for them.