I have just checked coupons. The lowest price I could get is 16.49 USD for MUSTOOL MT109 Multimeter (in Banggood). You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
Latest coupon code price check (UTC time):
Banggood (16.49 USD)
Banggood warehouse is located in China. Hmmm… There is no active coupon in Banggood at this moment. Is it cheap? It looks like it’s a good price (lower than average (17.32 USD)).
Link: Banggood product page
Price: 16.49 USD
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): d67c25, FinMustool, aef215, 502C6B, 15ANENG, BG2050, BGBG4683, d459b8, 0e7f33, FBCOUPON1, BGherra, BGMT109, BGGines, BG61957f
(these coupons are old, so probably won’t work)
Aliexpress
Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for MUSTOOL MT109 Multimeter is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).