Just check coupons out (with price alert and history). Best price?
Materials: ABS, 10 – 20 pcs AA size, 8 – 15 pcs AAA size, 5pcs C size, 4pcs D size, 2pcs 9V battery and other parts (such as – battery tester or small flashlight, etc).
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 code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
1. ($10.26): 13f142
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 and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): e2bcea, elec, AFfbG10, 502C6B, BGBFAFF2019, BGCITYADS2019, BGE13, BGVDay10%off, BGAFF10OFF, BGTT10, bGhOnEy10, BGdragonBoat, BGSS10%SW, bgshOOp10, BgoFErTaSchInA10, BgcLuBofErtA10, BGCuponation10
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for AA AAA C D 9V Battery Case.
Price records source(s): Gearbest, 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)).