Chiming in here - I too live near Belvoir obviously (as I’m married to Typo Knig). Our house was bought for 500K in 2002, we had one tax evaluation as high as 680K, but it’s down to just above 600K. This is in the Kingstowne subdivision, which is about a mile west of the western edge of Belvoir, in zip code 22315. A slightly larger house on our street just sold for something like 670K. Our subvision tends to be somewhat pricier than some surrounding areas, but you could find something lower-priced very near especially if you don’t want a McMansion. Also there are a lot of townhouses available, and you can get something pretty nice for less than 500K.
Look in zip codes 22315 and 22310. Also look around the Route 1 corridor and anywhere along Telegraph Road; also look in the Franconia area of the county; it’ll be listed as Alexandria for postal purposes, but is not Alexandria city. Also look in Lorton which has a lot of newer development. Some areas around route 1 aren’t necessarily the nicest - it’s strip-development hell - but you can go a few blocks off of 1 and get to some nice houses.
Second what others have said about not living on the Maryland side. Housing is a lot cheaper there, but it’s Prince George’s County. There are many nice areas of that county, but there are some bad ones, and it’s not a good commute. Only one reasonable way to get to Virginia from the MD side - the Wilson Bridge - and there are bad backups there pretty much every day.
The nicer areas are not near the Wilson bridge (well, going down route 210 you can get into some nicer areas, but there’s a horrible drive north bound to get to the beltway to get to VA). The schools aren’t as good, on average; if that’s not an immediate issue for you, it’s surely an issue if you’re hoping to resell at some point.
Feel free to PM either Typo or me; we may not be the closest Dopers to Belvoir, but we’re probably in the top 10.