$89.99 – RD6018 or RD6018W.
I have checked all old coupons and price is $89.99 for RIDEN RD6018 RD6018W USB WiFi DC to DC Power Supply (in Banggood). Just check coupons out (with price alert and history). Do you want to know what the best price is?
Latest price update (UTC time):
Banggood ($89.99)
Banggood warehouse is located in China. I’m afraid that there’s no working coupon in Banggood. Low/high price? Well, this price is higher than average price ($62.49)
Link: Banggood product page
Price: $89.99
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BG6918W, BG6018, BG6318W, BGRUMB15, BG73RD18, BG67RD, BGSTUDENT10, BGCuponation10, BG0646, BG16RD18, BG6018RD, 7bcdf9, BGab95d4, BGVNRD01, BGbabe19, 13f142, BGab91d4, BG7894ce, BG00c906, Terence, BG1efeb0, BGPL18MAJA0, 8wEbgaInS5, BGPL19MAJA0, pROMo8cuPoN, hoNEYbGdeAlS, BGJUNEGSG9, BG2c7a74, BGc52e1d, 9OFFSUMMER, Cuponation9, BGCOUPERT8, BGCAPITALOS8, BGESJY8, BGALL8
(these coupons are old, so probably won’t 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
Do you need price history chart (for all/most countries) for RIDEN RD6018 RD6018W USB WiFi DC to DC Power Supply? There we go. The lowest price was: $59.99.
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)).