According to my DB the lowest price is $36.79 for TRV06 Tuya Smart Zigbee3.0 Thermostat Radiator Valve (in Banggood). Price history, coupons and price alert are available on this page. Best price?
TRV06 Tuya Smart Zigbee3.0 Thermostat Radiator Valve Actuator Smart TRV Programmable Temperature Controller Voice Control with Alexa Google Home
Latest coupon code price check (UTC time):
Banggood ($36.79)
Banggood warehouse is located in China. There are no active coupons for this product, but the price is pretty low isn’t it? Is it a reasonable price for this item? Well, this price is higher than average price ($26.49)
Link: Banggood product page
Price: $36.79
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
Here is price history (for all/most countries) for TRV06 Tuya Smart Zigbee3.0 Thermostat Radiator Valve.
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)).