Aliexpress
Click here… to search for 4K Projector Screen 120-Inch on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I am tired of searching coupons, but I found one for you…
Link: Banggood product page
Coupon (17.99 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): BG589b2e
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for 4K Projector Screen 120-Inch.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).