Lens width: 60mm, Lens height: 52mm, Leg length: 150mm, Glasses width: 145mm.
Just check coupons out (with price alert and history). What is best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($47.73): bGhOnEy10
2. ($47.73): BGdragonBoat
3. ($47.73): BGAFF10OFF
4. ($47.73): BgcLuBofErtA10
you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): 34398b, aff7off, AFfbG10, BGMPB2020, BGSS10%SW, bgshOOp10, BgoFErTaSchInA10
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Other warehouses/versions
This item is available in 2 another warehouse/versions!
1. China – Xiaomi Anti-UV Polarized Sunglasses Grey ($-3)
2. China – Xiaomi Anti-UV Polarized Sunglasses Golden ($-3)
Price history and price alert
Price history (for all/most countries) for Stone blue Xiaomi Anti-UV Polarized Sunglasses is here. The lowest price was: $19.99.
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)).