Cost of Bay and Bow Windows. Bay windows are not cheap and the average price for a basic bay window can be anywhere from $1200 to $3000 for just the window. The cost of the bay window will depend on how large the window is and the materials that are used for creating the window frame.ow windows are great because they offer a bit more dimension and a unique look for any home. The average cost of a typical bow window is pretty much the same as bay windows or even slightly more $1400 to $3200.