According to my DB the lowest price is $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. What is best price?
Latest coupon code price check (UTC time):
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
Banggood ($20.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Is it a reasonable price for this item? From what I can see 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
(you can check these old coupons out, but these probably won’t 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
Price history (for all/most countries) for SONOFF D1 Smart Dimmer Switch is here.
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)).