The "Metered Connection" option in Windows 10 might help here, but as for websites you can't do much except using Ad blocker, "Disconnect.me" or Opera Turbo. (I'm not sure if Disconnect.me exists on opera).

Another way to mitigate would be to have the browser identify as a tablet/mobile as some websites assume mobile == metered connection. On top of my head, there is some addon like this in Chrome.