Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in Hong Kong. I am tired of searching coupons, but I found one for you…
Link: Banggood product page
Coupon (299.99 USD): BGfda478
(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): BGGRTK108, BGa372ce, BG648d61, BG272b86, BGef96eb, 2022ACTIESNL, CouponsdePC, BGfe4095, BGJUNEGSG9, BG8ReviTrage, Cuponation9, BGTKMN15OFF, BGTKMN20OFF, BG69c3a4, BgGoodie9, BG6fda43
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for TRIGKEY Speed S1 Mini PC i3-8109U 16/500GB is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).