I've lived in Fairfax County (Northern VA) for my entire life (I'm 20), and I don't know many details about the others, so everything here applies to Fairfax County alone. Also, this is just my common knowledge. I'm in no way a professional on anything here...
As far as houses go, 400k won't get you anything special. You could probably get one of the older homes in the more mature neighborhoods, which are actually pretty nice IMO depending on how many people you're living with. Said houses are decently sized (although it'd be difficult to find on with 4 bedrooms IMO), and said neighborhoods tend to have nice mature trees, bigger lawns, quieter streets, etc. A decent number of these houses have also been remodeled by the owners, although I don't know how many of those would be up for sale.
700K gets you into the low-high-end. You'd get one of the big, modern, cathedral ceiling houses. Unfortunately, the developers went fricken ape-shit into building these things, and some of these houses are literally 10 ft away from a heavy traffic 4 lane road. They also have no trees to speak of and much smaller lots (generally speaking). The houses themselves are pretty sweet though.
Most of the other houses are 1 mil+
As for neighborhoods, generally speaking, the further west you go, the better/more affluent the people get. Despite being the richest (average income/household) county in the country, there are still plenty of low-income areas you want to avoid. Most of said areas are in the east, but there are a few scattered out west (ie: around South Lakes High School). That said, crime/violence is defiantly low, especially in the west. I've lived here my entire life and I've only had 1 dangerous encounter. The main problem is Hispanic gangs, which are, one again, generally in the east.
As for within an hour of DC? Hahaha that depends on when you leave and the type of transportation. The DC metro system extends into much of Fairfax County (as far as Vienna currently, they're considering an extension to Dulles). It can get you to DC in 45 minutes or so, assuming you live in Vienna or don't mind driving/parking at the station. My dad drives to the Vienna station, take the metro into DC every morning. Works for him.
http://www.wmata.com/maps/metrorail_street_map.cfm
If you decide to drive, then I suggest you leave no later than 2 pm or no earlier than 7 pm if you want to get there in an hour. Rush hour's a bitch. Can't really avoid morning rush hour, unless you have a flexible job.
That said, everything you need will probably be within a 10-20 minute drive (depending on traffic). I have about 20 restaurants (from McDonalds to Olive Garden to McCormick and Shmit's (really nice expensive seafood place) (sp?)), 3 movie theaters, 4 grocery stores, 3 soccer fields, a hospital, a veterinarian's office, a Home Depot, an international Airport, a Bed Bath and Beyond and loads of other stuff within said drive.
While there aren't many "cities", there are Town centers which are the local hubs of activity
ie: Reston Town Center:
http://maps.google.com/maps?f=...1646,0.020084&t=h&z=16 (These pics are old. Most of the construction you see has been built up)
There are also plenty of large malls (Tyson's, Fair Oaks, etc)
http://maps.google.com/maps?f=...3306,0.040169&t=h&z=15
If you have kids and are looking at schools, there's currently a zoning war going on, so I'd wait until the dust settles there. Suffice to say I went through the public schooling system. It's the best in the nation, and it does deserve it. That said, some schools are fine, some are absolute ghetto trash (as in areas of the school owned by gangs after hours). Hence the reason for the current zone war (demographic distribution). However, I do know that schools I went to (Crossfield elementary, Rachel Carson Middle, Oakton High School) were and still are some of the best as far as public schools go. Chantilly high, Florence (sp?) elementary, and Madison High are also quality. Of course, we also have TJ (Thomas Jefferson High), the uber magnet private school, commonly rated as the best in the nation, despite the fact that Oakton, Chantilly, and Herndon IIRC actually competed in National robotics competitions (FIRST. Google it), when TJ did nothing of the sort. (Yeah, we all hate TJ
)
We also have a shitload of running/bike trails if you're into that. Most are scenic (through woods/trees, etc), and if the weather's nice they're highly enjoyable if you're into that. I cycled down the Fairfax County Parkway almost every day during the Spring/Summer.
http://www.fairfaxcounty.gov/nmtc/maps.html
Oh, BTW, I live here, in case you're curious:
http://maps.google.com/maps?f=...84&t=h&z=16&iwloc=addr
That's everything off the top of my head. Hope I helped.
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