Order through any Alexa compatible device and say "Alexa, order an Amazon Smart Plug" (I did this on my iPhone's Alexa app)
Once you do that, the smart plug will be automatically be added to your Amazon cart.
Now, go to Amazon and add an Echo Dot (3rd Gen) to cart for $22
At checkout, your total will be around $13 for both.
(I had to change the color of my Dot from black to white. The black one was saying it was unavailable.)