Latest update shows that 300m WiFi Repeater Signal Booster costs $13.99 (in Banggood). Price history, coupons and price alert are available on this page. Let’s see what best price is ATM.
Latest coupon and price update (UTC):
Packing: 11.7cm * 11.7cm * 6.7cm., Name: 300M WiFi Repeater, Product: 8cm * 5.2cm * 7.5cm., Color: white / black, Technology: white glossy surface, Material: shell ABS
Banggood ($13.99)
Banggood warehouse is located in China. I can’t find any active coupons for this product in Banggood. I think you want to know if the price is good. From what I can see this price is higher than average price ($12.49).
Link: Banggood product page
Price: $13.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGae2847, BG589b2e, BGcb5ddb
(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
Here is price history (for all/most countries) for 300m WiFi Repeater Signal Booster.
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)).