Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. We have found one coupon for this product!
Link: Banggood product page
Coupon (84.59 USD): BGAProjector
(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): BGA4300, aff7off, BG3CSUM, bgssaff9, BGPAYPALSS, BGaDmITAd, 7bcdf9, BGBR4300, BGCITYADS2019, bGpAnDacHeCk, Email5, BGAFF10OFF, bGhOnEy10, BGdragonBoat, bgshOOp10, BgoFErTaSchInA10, BGAFF7OFF, 7d18f7, 13f142, BGProjectors
(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 BROOK A4300 Projector.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).