I'm a General Contractor and a Broker ,and also leave in RWC. Whoever gives you a figure needs to keep in mind,if you going to have a bathroom or a kitchen in your addition, is your land flat or retaining walls will be required, what kind of roofing willl you have (weight of roof). The best answer (dollar figure) will be after you will produce some kind of ideas what are you planning to have . My suggestion to hire an architect, create prelim. drawings and the architect will give you figures.
If you need an honest contractor, call PJ Rielly at 415-317-3731. If he gives you a bid, he will stand behind it. Whoever you choose to do the job, never pay any contractor in full until the job is finished.
Dave Tap Tapper