Aliexpress
Click here… to search for 2x Sofirn 3.7V 3400mah 18650 Battery on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (12.83 USD): BGSF
Coupon (13.58 USD): BGTORCH
(CouponsFromChina.com tip: 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
Old coupons (from the oldest to the newest): FIN18634, linepayflt, EYBG, BGBSPX, 502C6B, BGBFCR41, bGhOnEy10, bgshOOp10, BgcLuBofErtA10, BGFLS15
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Do you need price history chart (for all/most countries) for 2x Sofirn 3.7V 3400mah 18650 Battery? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).