All other 4K set top boxes are $100 or more and this supports google cast too (can act as chromecast).
There's been a rumor than Google Chromecast ultra with 4K support may be announced on Oct 4th for $69 but this comes bundled with a remote and runs android TV (i.e. you can presumably install android apps). I'm not sure what Chromecast ultra will run.
Looks like you can place an order for store pickup now.
Mi Box Android TV
Quote :From Xiaomi USA:
"Mi Box starts selling in Walmart stores on October 7"