Steam just started their annual Autumn sale, which will last from today, the 23rd, to the 29th. During the sale, you can catch most of the newer TES titles for 50-73% off, as follows:

The newly-released Skyrim Special Edition will not go on sale at this time. GOG is not currently hosting sales for any of the older games in the series, but this blog will be updated if that is changed.

EDIT: The Skyrim – Special Edition is currently 25% off on Steam, and the Bethesda Store is also hosting a sale.