Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. There is one coupon available! Pretty cool, huh?
Link: Banggood product page
Coupon (311.39 USD): BGProjcc
(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): BGCTD97, BGAProjector, BGprtecmundo, BGVSFHG, BGALIBUYJ210, BGAudioVideo, BGProj, BGANFBW, BGcd428e, BGJNC11, BG589b2e, BGSaleFeb8, BG59a0d8, BGe713b9
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for ThundeaL TD97 Projector 1080p is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).