For a list of the different communities within Ashburn and the rest of Eastern Loudoun County, check out this post on my blog - http://realdiablog.typepad.com/loudounstats/2007/07/links-to - as well as other posts under the "Buyer Resources" category.
Certain areas of Eastern Loudoun County have shown more appreciation than others over the years as well as more depreciation over the last 2 years than others. Some are stable while others are still coming down in price.
There are definitely single family homes in the price range you're looking for, but only in certain areas of Sterling and Ashburn. They range in styles from ramblers and split levels to traditional colonials.
If you would like to chat more, feel free to email me - email@example.com.
I would also find a Realtor who is intimately familiar with the area. One whom I would trust for guidance is Lenn Harley at http://www.homefinders.com