Answers

The labor should not be more than $100-$200 per window depending on who you hire to do the job, the size of the opening, and accessability. The cost of the sash varies greatly depending on the window. First thing I would do is to check to see if warranty covers the window, if so, you may pbe able to get the sash for free. 

There is a lot of good advice in people's responses. The best thing you can do is get as much detail as possible in your estimate from your contractor/s. Just to clarify one myth, we, like most professionals, value our time. If a job takes 30 minutes to drive to, this time has to be accounted for in the management of the project. We, being a Contractor, charge more to manage a job that is half an hour from our place of business than we do a job that is 5 minutes away. Just to be fair, it cannot be said as a flat out fule of thumb that Contractors should not charge more solely due to location alone. You should never pay more because you are in a fancier neighborhood with the same logistics as the one next door. Just take it all into consideration during your search.

As Brittany stated earlier, we only use hot-dipped galvanized in this application. It is not a code issue but it does make a huge impact on quality and what will be seen for years to come.