Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. We have found one coupon for this product!
Link: Banggood product page
Coupon (18.82 USD): BGherra
(CouponsFromChina.com tip: apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
There were country-specific coupon codes published on Couponsfromchina social channels and price alerts. Coupon price may vary by country, because there’re different VAT rates, shipping cost etc. There is a chance that some latest coupons are still working:
Old coupons (from the oldest to the newest): bgsport, FinMustool, a62237, c2b135, AFfbG10, bGhOnEy10, BGAFF10OFF, BGM66, 13f142, BG11SHOP
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Price history (for all/most countries) for MUSTOOL MT66 Multimeter is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).