Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (426.35 USD): BGPROBuscape
Coupon (451.43 USD): BGAProjector
(CouponsFromChina.com tip: coupon code has to be applied in shop’s cart 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): BGaDmITAd, aff7off, bgchinafest, BGBFAFF2019, BGCITYADS2019, Email5, BGAFF10OFF, bGhOnEy10, BGdragonBoat, 7bcdf9, bgshOOp10, BgoFErTaSchInA10, BGAFF7OFF, BGProjectors
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for UNIC UC46 Mini EU Plug Projector is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).