Recently, I replaced 11 windows of various sizes in my in-laws old house. The new windows come from Home Depot and are double-layer, gas-filled, Low-E coated, energy efficiency vinyl windows. In addition to the thermal transfer improvements, the sound dampening is impressive. Overall (with Pro discount) all the windows and materials cost me around $1600 total. We saved a ton of money doing it ourselves (though they did take at least 6 weeks to arrive). My father helped me with 2 of them, and my nephew helped me with the rest. It turns out windows are very easy to replace lol They are pretty much only anchored with a few screws and then caulked into place. You can use an x-acto blade to cut the caulk, remove the screws, and the old windows will usually pop out pretty easily. Then it’s just a matter of reversing the process with the new windows. Because the house was very old (historic) and the window frames were non-standard, we had to sand down some of the sills and insets to get some of the windows to fit properly. But a newer house shouldn’t have this problem.