Aliexpress
Click here… to search for eSUN 405nm Water Washable 3D Printer Resin [EU] on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in Europe 
. I don’t really know if this price is reasonable, coz there’s no price history in my DB.
Link: Banggood product page
Coupon (9.99 USD): 1673bd
Coupon (9.99 USD): c2f567
(CouponsFromChina.com tip: coupon code has to be applied in shop’s cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Price history and price alert
Price history is not available for this item (not enough database records)! The lowest price was 9.99 USD though.
You can set price alert (for Banggood).