Aliexpress
Click here… to search for Opus BT-C100 Battery Charger EU Plug on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
Coupon (23.38 USD): BGTorch4
(CouponsFromChina.com tip: apply code in your basket (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): linepayflt, EYBG, BGTORCH, MOPU1, 502C6B, BGBFCR02, BGBFCR41, 0e7f33, FBCOUPON1, BGFLS15, BGAFF10OFF, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel, 4BLF, BG10OFFAFF1, BANGGOODSD, 6GSGIT
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for Opus BT-C100 Battery Charger EU Plug is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).