Even Andersen windows which are solid wood with solid wood frames are not that expensive. The normal price for an Andersen window is prox $300 a piece plus installation. The only thing that should make them expensive is if you have to alter the opening to get them to fit. Depending on your interior trim, if you have to replace it then the costs rise. The out side trim could become expensive also. This is not rocket science and a lot of contractors would have you believe that it is.
If you are replacing size for size the normal installation of a window should only take prox 1 hour per window with one man. I still can't get over that $21,000 price tag, what a rip.