J.M.
The window tinting is Mylar, just like for car windows, and it comes in various thinkness and degree of tint, both of which affect the cost. We have used it for years. You can ask a window tinting shop and they will probably do your home windows. The one known problem is that if your windows have a partial vacuum and a gas inside (modern windows have this), then there is a legal limit as to how heavily you can tint them because the tint, on the inside, will cause the gas to overheat and this harms the window. We installed all new windows, a light Mylar tint on those windows exposed to the sun, and cut down dramatically on the heat from the sun. Curtains or vertical blinds then take care of the rest, and our house is cool again, even in summer, without extremely high electric bills. Your power company will probably do a free energy audit, which will show you other ways to reduce your electric bill too.