Basically copy coupon, view price history or create e-mail price alert. What is the best price?
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):
Printingsize 220*220*250mm, LayerThickness 0.1-0.3mm, Printingresolution ±0.1mm, Printing speed 20-150mm/s, Hot bed temperature(Max) 100℃, Movement speed 10~300mm/s, Extruder working temperature(Max) 250℃, Standard nozzle diameter 0.4mm
Banggood
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): Wholesale20, Email5, 7d18f7, BGESET4PRO, BGHALLOWEEN, 13f142, 2022ACTIESNL, 8Couponsde, MVC8SPRING
(I don’t think these’re gonna work, but you can try ’em out anyway)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – Anet ET4 Pro 3D Printer [EU] ($-3)
Price history and price alert
Price history (for all/most countries) for Anet ET4 Pro 3D Printer is here.
Price records source(s): 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)).