Aliexpress
Click here… to search for Mini Size Inner Ear Invisible Hearing Aid on 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 (11.89 USD): BG75597c
Coupon (12.73 USD): Cuponation9
Coupon (12.87 USD): TTSUMMER8
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): BG9cc7f2, BGHB218, BG785c81, 2203ActiesNL, BGHECARE1, BG4ee866, BG14c65e, BGa39f8d, 9OFFSUMMER
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for Mini Size Inner Ear Invisible Hearing Aid.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).