Communication method WIFI 2.4G, Weight 70g, Power supply mode DC 4.5V (3 AAA batteries), Working temperature -10~+55℃ 0~100%RH, Size 65x60x26mm/2.51×2.36×1.02in, Material ABS/PC.
Basically copy coupon, view price history or create e-mail price alert. What is the best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($22.47): BGAlerabat1
2. ($24.85): BG00c906
paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): BGTY071, BG10OFFAFF1, BGTYOC071, BANGGOODSD, 6GSGIT, BGPA071, 00c906
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Check out price history chart (for all/most countries) for Tuya Smart WiFi Temperature Humidity Sensor. The lowest price was: $16.99.
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)).