Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. There is one coupon right now! Check this out.
Link: Banggood product page
Coupon (135.99 USD): 7bcdf9
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply 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): 85061c, 502C6B, PICODICOM, TECH8%, aff7off, BG3CSUM, bgssaff9, BGaDmITAd, bgchinafest, BGBFAFF2019, BGCITYADS2019, bGpAnDacHeCk, BGMPB2020, Email5, bGhOnEy10, BGdragonBoat, BGAFF7OFF, bgshOOp10, BgoFErTaSchInA10
(there’s a little possibility that old coupon will work)
Price history and price alert
Price history (for all/most countries) for Houzetek M2 4500lm Projector is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).