According to my DB the lowest price is $99.99 for Tuya Smart WiFi Home Alarm System Kit (in Banggood). Just check coupons out (with price alert and history). You probably want to know what is the best price?
Latest price update (UTC time):
Relative humidity: <80%Rh (no condensed), GSM system: 850/900/1800/1900MHz, Reserve battery: 3.7V/500mAh lithium battery, Work temperature: 0 ~ 55 ℃, Alarm number output: <500ma, Working voltage: <120mA, Wireless frequency: 433 MHz, Wireless code: EV1527, The current of the aircraft: <10UA, Input voltage: DC5V (Microusb standard interface power supply), WIFI system: IEEEEE802.11b/g/n wireless standard
Banggood ($99.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Low/high price? Maybe there’re no more promotions for this item, because current price is higher than average (which is equal $84.99)
Link: Banggood product page
Price: $99.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG4e7b81, BGSaleAD, BG92f5fd, BGMARCHSALE, BGAUGUST8, BGCAPITALOS8, BG8FORMULAMX
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
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
Check out price history chart (for all/most countries) for Tuya Smart WiFi Home Alarm System Kit.
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)).