Just check coupons out (with price alert and history). Do you want to know what the best price is?
Resolution Support: 4K, 4: 3, Display type: DLP, Contrast Ratio: 3000: 1, Throw Ration: 1.28: 1, Image Scale: 16: 9, Image Size: 28 – 180 inch, Projection Distance: 1.20m-6.0m, Brightness: 6800 ANSI Lumens, Native Resolution: 1920x 1080
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
1. ($613.79): BGAProjector
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 and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): TECH8%, aff7off, BG3CSUM, BGaDmITAd, bgchinafest, BGBFAFF2019, BGCITYADS2019, bGpAnDacHeCk, Email5, bGhOnEy10, BGdragonBoat, BGAFF7OFF, bgshOOp10, BgoFErTaSchInA10, BGAFF10OFF, 7bcdf9, BGProjectors
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for VIVIBRIGHT J10 Mini DLP Projector.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).