I have just checked coupons. The lowest price I could get is $14.99 for Tuya Zigbee Smart Knob Scene Switch Button (in Banggood). Basically copy coupon, view price history or create e-mail price alert. Let’s see what best price is ATM.
Latest price update (UTC time):
Tuya Zigbe Smart Knob Wireless Scene Switch Button Control Dimmer Battery Powered Automatic Scene Smart Life APP
Banggood ($14.99)
Banggood warehouse is located in China. Hmmm… There is no active coupon in Banggood at this moment. Is it cheap? From what I can see this price is higher than average price ($13.49).
Link: Banggood product page
Price: $14.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Do you need price history chart (for all/most countries) for Tuya Zigbee Smart Knob Scene Switch Button? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).