This can very greatly on type, views, location, condition and overall size of the unit.
If you look at a recent 2400 square foot townhome resale for $538,000, dollars per square foot come out to roughly $225. Some of this square footage is on the lower level.
On a recent new construction sale, a two bed two bath condo with great views closed at over $500 per square foot.
Before making an offer, search out the most comparable closings you can find to help you determine value.
Best of luck.