Just check coupons out (with price alert and history). Let’s see what best price is ATM.
Model Number: Sanyo UR18650ZY Feature: Convex head design Capacity: 2600MAH Nominal Voltage: 3.6~3.7V Internal resistance: 35~50milliohm Color: Red and purple head Weight: 49g/pcs Size: (DxL) 18×65 mm
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. There are no active coupons for this product, but the price is pretty low isn’t it?
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): 502C6B, e2bcea, linepayflt, EYBG, BGTORCH, BGBFCR41, bGhOnEy10, bgshOOp10, BgoFErTaSchInA10, BgcLuBofErtA10, BGFLS15, 4BLF, BGAFF10OFF, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel, BG10OFFAFF1, BGFLBA, BANGGOODSD, BGTorch4, 00c906, BGtorch2, BGtorch3
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for 4x Sanyo 3.7V 2600mAh UR18650ZY 18650 Battery 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)).