Depending on size and features, the price could range from $200/ sq ft and upAlways check references before building. Check out this website which can give you an idea about plans and cost. http://homeplans.familyhandyman.com/index.aspx
I would have to agree with Lisa on this one. $250 does build you a very nice home (not including land), but the type of luxury homes in Osterville I think of are more in the 500 per square foot range....and up.
You have the right Realtor for this answer. I happened to be married to a builder. Average cost is 500 to 600 a sq ft. not including the land. If your taste in luxury is extremely high end you could even be looking upwards to the 1000 per sq ft avg. If you need more information feel free to contact me.