I have just checked coupons. The lowest price I could get is 4.89 USD for ETOPOO 150mm Mini (in Banggood). Basically copy coupon, view price history or create e-mail price alert. You probably want to know what is the best price?
Latest coupon code price check (UTC time):
Banggood (4.89 USD)
Banggood warehouse is located in China. I’m afraid that there’s no working coupon in Banggood. I think you want to know if the price is good. This price is higher than average price (3.84 USD) for this item.
Link: Banggood product page
Price: 4.89 USD
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Aliexpress
Click here… to search for ETOPOO 150mm Mini Plastic Caliper on Aliexpress
Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for ETOPOO 150mm Mini Plastic Caliper.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).