Insulated glunitsalsoed thermopane windows have double panes of glseparated and sealed to create air pockets. But how much does it cost to replace them?.How much replacement windows should cost. Average costs and comments from CostHelper’s team of professional journalists and community of users. Expect to pay an average of $ $ per window for replacements placed inside existing and structurally intact window frames, but it could go as high as $, per window, for a range of $, .The size of your house, or more specifi.y the number and size of windows that are being replaced, is the biggest single factor in determining the overall cost that you will pay for replacement windows.Replacement window costs are always at the top of the list for any homeowners planning to renovate or upgrade theier home windows. While the cost of replacing your windows can seem overwhelming at first glance, there are some nice benefits that will help ease the sticker shock..