Just check coupons out (with price alert and history). What is the best price?
USB output: 5V/3A, Discharge stop: 21.4V, Float charge: 27.4V, Voltage: DC 12V/24V, Self-consume: <10mA, Buck charge: 28.8V, Current: 10A/20A/30A/40A, Model: PWM, Output voltage: 12V/24V Automatically distinguish voltage, Working temperature: -35℃~60℃, Rated working current: ≤20A, Discharge reconnect: 25.2V, Max solar input: <50V
Aliexpress
There’re some similar (or not) items on Aliexpress
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 Europe 
. Hmmm… There is no active coupon in Banggood at this moment. Sorry, but there’s no price history 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!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG42df5e, BG589b2e, BGET10
(there’s a little possibility that old coupon will work)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. China – 50A 12V/24V Solar Charge Controller ($17.54)
Price history and price alert
Price history is not available for this item (not enough database records)! The lowest price was $15.79 though.
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)).