Brand Name: Gemfan, Quantity: 2 CW + 2 CCW, Mount: M5, Pitch: 3.6in, Recommend Quad weight: 450g-600g, Inch: 5.15in, Recommmend Adaptive Motor: 2207 and up, Weight: 4.3g, Material: PC.
You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
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.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($5.22): Cuponation9
2. ($5.28): BGRCParts8
apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BG8RCToy, BGJUNEGSG9, BGRCT10
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Do you need price history chart (for all/most countries) for 2 Pairs Gemfan Vannystyle 5136 5.1×3.6 5.1 Inch 3-Blade Propeller? There we go. The lowest price was: $5.17.
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)).