Looking to understand cost per square foot to go up one level?

We are looking to add additional 900 sq sf with a second floor. We would like it to have theee bedrooms and a bathroom.

So far we saw two builders (we are located in NH Lakes Region) and they said $350 a square foot. i know things are expensive but this prices us out of our house. As first floor needs works so we are looking at $630,000 for a second floor addition. We bought this house for $640,000 four years ago….

is this accuract or did we just talk to wrong contractor?