You can't buy a NOW branded box because they are no longer made.
My recommendation is to buy a Amazon Fire stick or Roku stick. Have a nosy at this link for all supported devices.
Sure, if you’re crazy, and have money to burn.
The Now devices on Amazon are old models, or wildly overpriced, and often both.
Up to date devices that will run Now, if you need one, can be obtained from Amazon sure - by buying an Amazon Firestick, or a Roku Express or Stick. For between £20 and £50, depending on how fancy you want it; although a £20 Full HD Firestick will suffice for Now, other apps on these devices can offer 4K, which the over-£20 sticks can support.
There is no future, literally, in Now-branded devices 😢
Now Boxes are stripped down Roku devices running custom "now"branded firmware.
for the same experience get a Roku device .
I own both Roku and Fire, and my preference is Roku due to its cleaner interface and all apps listed in a grid as opposed to Fires busy ui aimed at selling amazon content
Either which way i would advise against buying the budget entry models