$7.99 – Product color: white, Directive rate: 0-9999US/cm, Accuracy: ± 2%, Net weight: 55G, TDS: 0-9999ppm, Celsius: 0.1-80.0 ℃, Fahrenheit: 32.0-176.0 ℉, Size: 154 × 30 × 14 (mm).
You can get TDS Meter Water Tester 0-9990ppm for $7.99 using coupon code (in Banggood). Just check coupons out (with price alert and history). Let’s see what best price is ATM.
Latest coupon and price update (UTC):
Banggood ($7.99)
Banggood warehouse is located in China. There are no coupons for this product in Banggood. I think you want to know if the price is good. Maybe there’re no more promotions for this item, because current price is higher than average (which is equal $5.22)
Link: Banggood product page
Price: $7.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): BG0ed120, BGXIFD397, BGM1TOOLS88, BG896e50, BG1e01af, BG7a373e, BG051f88, BGTOOS729
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
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
Price history (for all/most countries) for TDS Meter Water Tester 0-9990ppm is here. The lowest price was: $4.96.
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)).