Can't say if it applies there, but here they are getting about 6-7 dollars/sq ft, sometimes more and rarely less. Includes, the frame, exterior windows and door install, stair install and soffits and fascia's.
There may be a reason why they vary widely and they're mostly devious.
My one and only experience with having something built was 2 years ago (a somewhat large two-car garage). I made a list of my requirements (a wish list) and found a draftsperson to create a set of plans (for < $200!!! - the best price from an architect was $2500!!). I wanted the 'experience' of getting the plans approved so I took them in myself to the building department - took one hour and got the required permits - I was quoted a minimum 0f $500 PLUS the cost of the permits if the contractor did it!!!
I made 10 copies of the approved plans and got bids from 9 contractors (I gave them a copy of my requirements and a set of plans and asked each one to submit a bid in writing with my requirement spelled out in the contract. Three contractors gave me verbal bids only (never did submit anything in writing) and they came in 'low', two bidders weren't even licensed though their business cards showed a 'license number' (in California, you can check this using the internet), one guy came in real high and the remaining three bids were real close to each other (within $2000).
I automatically tossed out the non-licensed bidders, those that gave me verbal bids only (these are a recipe for guaranteed future disputes) and the real high bidder (he obviously didn't want to do the job). The remaining three presented themselves professionally, gave me a bid with what they will do for that money which included my rerquirements and gave me references. I probably would have been happy with any of them and the one I chose did a great job and have recommended him to others.
In summary, by getting a lot of bids, I saw a 'trend' in bids and was able to select from what I consider the only three worth doing business. I saw, as you have, that the bids were all over the map and I believe I found out why.