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. 

It depends on the type of window.  Is it just a glass replacement or does really need the entire sash?  Sometimes, the I.G. unit can be replaced using the same frame.

It all depends on the type of window, that being said many newer winodws come with warranties that would incluide replaceing a damaged sash free of charge. However a safe estimate for a standerd vinyll window sash replacemant will cost around $175.00