$23.99 – Power supply: 2x AAA 1.5V battery(not included), Measurement: double integral A / D conversion, Sampling rate: about 3 times per second, relative humidity<80%, Volume (size): 142×70×32mm(L×W×H), Display: Black EBTN screen, Overrange display: the most significant bit was "0L", Maximum display: 9999 (3 9/10) bits automatic polarity display, Working environment: (0~40)℃, Low voltage display: Yes.
I have checked all old coupons and price is $23.99 for MUSTOOL MT109 Multimeter (in Banggood). Just check coupons out (with price alert and history). You probably want to know what is the best price?
Latest price update (UTC time):
Banggood ($23.99)
Banggood warehouse is located in China. I’m afraid that there’s no working coupon in Banggood. Is it cheap? This price is higher than average price ($17.32) for this item.
Link: Banggood product page
Price: $23.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): d67c25, FinMustool, aef215, 502C6B, 15ANENG, BG2050, BGBG4683, d459b8, 0e7f33, FBCOUPON1, BGherra, BGMT109, BGGines, BG61957f, BGMAI666
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Check out price history chart (for all/most countries) for MUSTOOL MT109 Multimeter. The lowest price was: $15.99.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).