I have worked with many home owners and Investors who have added square footage and/or done improvements. I am working with one investor who is building a house in Pleasanton. Depending on the contractor and the city, price can rage anywhere starting from $100 SqFt. My client uses a contractor and depending on the project he charges around $150/ SqFt.
The basic price for the actual construction will be in the neighborhood of $225-$250 a sq/ft, plus building fees, architect, foundation reinforcement and SO much more. Depending on the final outcome, your costs could be as high as $450 sq/ft.
You can find a good contractor through sites like Angie's List or Service Magic.
Concurrently, he should engage a structural engineer or construction professional to determine if the current structure can support a second floor.
And as a general resource, check out Remodeling Online's Cost vs Value in the area
Here's the link
And whatever your friend finds out and decides to do, he should make sure that he gets his contractor to pull permits for the renovation, etc.