Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (19.54 USD): BG75597c
Coupon (20.92 USD): Cuponation9
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGf109e2, BG43785b, BGHECARE1, BG4ee866, BG6b3867, 9OFFSUMMER
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Price history (for all/most countries) for TENS Unit Electronic Pulse Meridian Massager is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).