Sutra is excellent and in your price range, but if you are going for romantic, may not be the best option as you share a table with other guests.
As others have said, Cafe Flora is one of the city's best, but is in no way healthy.
I am a also a huge fan of Carmelita. I have taken my lady here on a couple of dates, and always leave extremely impressed. Yes, it's a 'neighborhood' joint, but its small, quiet, and very romantic.
One that hasn't been brought to the list, and is a personal favorite for date night is the Plum Bistro on Capitol Hill. It is pretty loud, but the food makes up for the noise. I could not recommend this place enough.