$15.99 – 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.
ATM you can buy SONOFF D1 Smart Dimmer Switch for $15.99 (in Banggood). Go down and check coupons out. Remember to check price history if it is available. What is the best price?
Latest coupon code price check (UTC time):
Banggood ($15.99)
Banggood warehouse is located in China. There are no coupons for this product in Banggood. Price? Well, this price is higher than average price ($9.62)
Link: Banggood product page
Price: $15.99
Additional Banggood coupons: first page and second page
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
(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
Check out price history chart (for all/most countries) for SONOFF D1 Smart Dimmer Switch. The lowest price was: $9.34.
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)).