Adding 2nd floor/storey - how much does it cost?

We live in Vancouver and we'd like to add (put back) the 2nd floor of our almost 100 year old house. Right now what used to be the 2nd floor of our house is just a huge sundeck but it used to have bedrooms and bath upstairs. I've talked to a couple contracting companies and it seems like it's going to be around $150 on average (depending on finishes). We're only adding on about 500-600 sq ft at most so that's coming out to $250 a sq ft. Isn't that high?

Would contracting companies be willing to only take the project to something like drywall and rough in plumping stage and we'd finish things ourselves --- the 2nd floor would just be 2 bedrooms and 1 bath.

And finally, it would be great if anyone recommend any contractors that they've worked with and done good work with additions in the Vancouver area. Thanks.