Amazon offers its Prime members the Valve Steam Link for $19.99 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $4.98.) That's tied with our mention from six days ago, $30 off, and the lowest total price we could find. It streams games from your PC to your TV and is compatible with Steam, Xbox One, and Xbox 360 controllers.
It's currently on backorder, but can still be purchased at this price.
Of note, Gamestop offers it for the same price via in-store pickup.