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 (513.03 USD): BGLaurent
Coupon (524.69 USD): BGAProjector
(CouponsFromChina.com tip: apply code in your basket (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): BGWoH101, aff7off, BGaDmITAd, bgchinafest, BGCITYADS2019, bGpAnDacHeCk, Email5, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGAFF7OFF, bgshOOp10, BgoFErTaSchInA10, 7bcdf9, BGProjectors, BGPROBuscape
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Wowoto H10 DLP Projector.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).