Summer sale is June 27th. I would expect it to go on sale then. You can also keep an eye on deal.gg and see if you can get a key elsewhere. Buy at your own risk though as most of the sites on there are key resellers with unknown origin how they got them.
Only works if you haven’t updated it since the February 2021 update. You also would lose the actual built in Chromecast feature.
Cool but I don’t really see why you would do it on this device when you can just flash android to a raspberry pi or something and have basically the same thing at that point.