Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (26.49 USD): BGPTL088
Coupon (28.05 USD): BGGines
Coupon (29.30 USD): BG00c906
(CouponsFromChina.com tip: this code has to be applied in your cart 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): BG8a2188, BGherra, BG059eeb, BG405c12, CityadsTool
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for S-170 480x318mm Silicone Soldering Pad is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).