Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. We have found one coupon for this product!
Link: Banggood product page
Coupon (415.99 USD): BGd2c247
(CouponsFromChina.com tip: just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
There were country-specific coupon codes published on Couponsfromchina social channels and price alerts. Coupon price may vary by country, because there’re different VAT rates, shipping cost etc. There is a chance that some latest coupons are still working:
Old coupons (from the oldest to the newest): BGSaleFeb8, BG79901b, BGSaleAD, BG81987e, BGae2a63, BGadce83, BGc405c1
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for TOPSHAK TS-PS1000 1100Wh Li-ion Power Station.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).