When I was updating this page, then coupon price was $20.99 for SONOFF D1 Smart Dimmer Switch (in Banggood). Go down and check coupons out. Remember to check price history if it is available. Do you want to know what the best price is?
Model: D1, RF band: 433.92Mhz, Enclosure material: PC V0, Output: 100-240V AC 50/60Hz, Input: 100-240V AC 50/60Hz, Dimension: 62*47*32.5mm, Wi-Fi: IEEE 802.11 b/g/n 2.4GHz, Dimmable LED: 150W, Incandescent bulb: 200W, Max. current: 1A
Latest coupon code price check (UTC time):
Banggood ($20.99)
Banggood warehouse is located in China. There are no coupons available at this moment in Banggood. I think you want to know if the price is good. Well, this price is higher than average price ($9.62)
Link: Banggood product page
Price: $20.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): elec, BGTT10, bGhOnEy10, BGSMOFF, BGSONOFF15, BGELIG0920, 13f142, BgcLuBofErtA10, BGSONOFFD1, BGSONOFF16, BGAFF10OFF, BGSTHO15, BGCuponation10, BGHONEY2110, BGSHOM15, 6GSGIT, ADMITAD2212, BGSmart6, BGe8f407, MVC8SPRING, 2203ActiesNL, BG15Sonoff
(there’s a little possibility that old coupon will work)
Aliexpress
There’re some similar (or not) items on Aliexpress
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 SONOFF D1 Smart Dimmer Switch.
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)).