$24.99 – WZ5020L DC-DC 50V 20A 1000W Buck Converter CC CV Step-down Power Module Adjustable Voltage Regulated Power Supply.
I have just checked coupons. The lowest price I could get is $24.99 for WZ5020L DC-DC 50V 20A 1000W Buck Converter (in Banggood). Just check coupons out (with price alert and history). What is the best price?
Latest coupon code price check (UTC time):
Banggood ($24.99)
Banggood warehouse is located in China. I can’t find any active coupons for this product in Banggood. But wait a sec… Is it a good price? From what I can see this price is higher than average price ($19.99).
Link: Banggood product page
Price: $24.99
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BG142c6e, BG589b2e
(there’s a little possibility that old coupon will work)
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
Here is price history (for all/most countries) for WZ5020L DC-DC 50V 20A 1000W Buck Converter. The lowest price was: $19.99.
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)).