Just check coupons out (with price alert and history). You probably want to know what is the best price?
Interface: USB2.0, Speed: 300Mbps, Dimension: 12x 3x 0.5cm, Weight: 35g
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($11.56): BGAFF10OFF
2. ($11.56): bGhOnEy10
put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): 502C6B, TTxBG10, BGRepeater, BG3CSUM, AFfbG10, BG455XM4C, BGCVTUY8N, BGBFAFF2019, BGhjiff5io, BGCITYADS2019, BGN355P
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi 300Mbps Wifi Amplifier Chinese.
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)).