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. Price history, coupons and price alert are available on this page. Do you want to know what the best price is?
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.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. I don’t think there is an active coupon right now – at least in my database.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): d67c25, FinMustool, aef215, 502C6B, 15ANENG, BG2050, BGBG4683, d459b8, 0e7f33, FBCOUPON1, BGherra, BGMT109, BGGines, BG61957f, BGMAI666
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (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)).