Basically copy coupon, view price history or create e-mail price alert. What is best price?
Max Charge Capacity: 300W, Power: 400W, Voltage Range: AC 110-220V, 0.1-3A(Internal consumption mode), Supported Batt. Type: LiFe/Lilon/LiPo/LiHv (2-8S), Charge Current: 0.1-15A, Current: 16.6A, Input Voltage: DC 10-30V, Discharge Current: 0.1-15A(Recycling mode), Output Voltage: 0-30V, Max Discharge Capacity: 20W, Size: 222×70×38.8mm, Weight: 668.5g, NiMH/Cd(1-20S), Pb(1-10S)
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.
Link: Banggood product page
1. ($53.99): BGAFF10OFF
2. ($53.99): bGhOnEy10
put item in your cart and apply coupon code there 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): BGToolkitRC10, affbg10, AFfbG10, 502C6B, BGCITYADS2019, BGVDay10%off, BG10BC, BGMPB2020
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for ToolkitRC M8 DC 300W 15A RC Battery Charger White With Power Supply.
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)).