The cost of a single upvc sash window is usually more than those for casement windows of the same dimensions, due to the complicated counterweight system employed by sash windows.
Because the key feature of sash windows is the way they slide up and down to open, they need some support to take the weight of the frames as they move – otherwise they would be difficult to open.
There is s system of ropes, pulleys and counterweights within the frames of traditional design sashes and a spring tension balance in some of the latest designs. This is how the weight is supported.
So, you will find that replacing a sash window needs some research to give you the opportunity to identify what the current market prices are and where to find the best possible deal at the time you are buying them –
in this instance you could go to this page and see what is going on right now: https://www.doubleglazingpriceguide.org.uk/can-you-buy-coloured-upvc-windows/