Just check coupons out (with price alert and history). What is 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 price update (UTC time):
Standby time about 180 hours, Color Elegant black, Charging Current 5V 120mA, Calling time about 16 hour, Playing time 5-6 hours, Horn power 50mW*6, Capacity 120mAh, Model MG10, Lens Features UV400 / Anti blue light, Impedance 16 ff, Charging time 1-2 hours, Microphone sensitivity -38dB36dB, Track Dual speaker stereo, Frequency Range 20~20000Hz, SNR ≥101dB, Frame Size 165*45*152mm, Frame Material Nylon TR90
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($50.04): Cuponation9
2. ($50.04): 9OFFSUMMER
coupon code has to be applied in shop’s 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/5cd
Old coupons (from the oldest to the newest): BGMG10, BG4061f4, BG17bf83, BGBuscape01, BGBRPL2, BGHOTSHOP15, BG53e9c8, Terence, Tabby20, BGd22fc4, BG6dc9f5, BG1efeb0, MVC8SPRING
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Lenovo MG10 Bluetooth Music Smart Glasses 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)).