I have just checked coupons. The lowest price I could get is $6.29 for 4 Pairs Gemfan 1636 1.6×3.6×4 40mm 1.5mm Propeller (in Banggood). Check coupons or create price alert down below. What is the best price?
Material: PC, Number of blades: 4-blade, Paddle disk diameter: 40.8mm, Weight / G: 0.61G, Maximum blade width: 7.46mm, Adaptation motor: 1103-1105 Recommended motor: 1103, Center hole inner diameter: 1.5MM, Pitch: 3.5in, Center thickness: 5.2mm
Latest price update (UTC time):
Banggood ($6.29)
Banggood warehouse is located in China. I have no active coupons for you right now. Is it cheap? Hmmm, price is higher than average (which is $4.77 right now), so better set price alert down below…
Link: Banggood product page
Price: $6.29
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): 10Gemfan, bgssaff9, AFfbG10, BG12MRP, BGGEPPart, BGVDay10%off, Parts8, BGAFF10OFF, BGTT10, bGhOnEy10, BGdragonBoat, BGSS10%SW, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10, BGDAVIS, BGHONEY2110, 13f142, BGGAL8, BGJON8, BGRCParts8, Tabby20, BG1efeb0, 8Couponsde, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BG8RCToy, BGRCT10, BGJUNEGSG9, TTSUMMER8, Cuponation9, BGMatt2022, BGToys8, BG589b2e
(these codes were not working in latest coupon update, but you can check them out anyway)
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 4 Pairs Gemfan 1636 1.6×3.6×4 40mm 1.5mm Propeller 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)).