I had Creative Windows out of Sterling do my townhouse in Centreville. I had 10 custom made windows, all double hung, low-e coated, argon filled and elligble for the 2009 tax credit. Total cost was $3500 even...included all taxes, etc. and take away of the old windows.
If you shop around you can find a little cheaper, but $3500 for 10 higher end windows isn't bad. They're Simonton windows too which are a nice mid to high level window.
http://www.creativewindowsva.com/
Oscar is the guy that helped me, he's not pushy and the owner of the company does the final measurements. Took them 3.5 hours to install and be gone. Painless.