Aliexpress
Click here… to search for Digoo DF-004 Portable Fan 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 (9.68 USD): BGDigoo15%
Coupon (10.59 USD): PICODICOM
(CouponsFromChina.com tip: 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
Old coupons (from the oldest to the newest): 50DGPO, 0404digoo, 930992, 3b393b, BGDIFAN
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for Digoo DF-004 Portable Fan.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).