You can get 2pcs Ultrasonic Pest Repellent for $12.99 with coupon (from Banggood). Price history, coupons and price alert are available on this page. Let’s see what best price is ATM.
Latest price update (UTC time):
2pcs Ultrasonic Pest Repellent 3-in-1 Triple Frequency 360 Degree Coverage Easy Installation Chemical-Free Safe for Pets and Children 800-1800 ft² – 2Pcs Black
Banggood ($12.99)
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. Is it good price? Well, this price is higher than average price ($9.49)
Link: Banggood product page
Price: $12.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGc192cb
(these coupons are old, so probably won’t work)
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
Price history (for all/most countries) for 2pcs Ultrasonic Pest Repellent is here.
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)).