Just check coupons out (with price alert and history). What is the best price?
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):
Model: MV20, DPI switching: 3-level DPI one-button switching, Product size: 117*76*69mm, Product weight: about 90g (without batteries), Color: Black, Ergonomics: vertical ergonomics, Connection method: wireless 2.4G, Working method: optical engine, Power supply mode: two AAA batteries (without batteries), Buttons: left button / middle button / right button / forward button / back button / DPI switch button, Name: 2.4G wireless vertical mouse, Battery life: about 9 months, DPI: 800/1200/1600DPI, Brand: Rapoo
Banggood
Banggood warehouse is located in China. There are no coupons for this product in Banggood.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGb9c2d3
(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 Rapoo MV20 2.4G Wireless Vertical Mouse.
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)).