Just check coupons out (with price alert and history). Best price?
Size: 51mmx 51mmx 12mm, Input Voltage: 4.8-6.0V, Gyro/Acc: InvenSense Inc., Signal from Receiver: 1520us (5 channels), Signal to ESC: 1520us, Weight: 21 gram (Inc Piezo buzzer), AVR interface: standard 6 pin, Item number: KK2.1.5, IC: Atmega, Auto-level: Yes
Aliexpress
There’re some similar (or not) items on Aliexpress
| Image | Product (link) | Price | Coupons |
|---|---|---|---|
 |
KK2.1.5 LCD Flight Control Board V1.19S1 PRO Self-Balancing Programmer FC for RC Airplane FPV Racing Drone DIY 1520us | $16.60 | – |
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. There is no active coupon in my database right now (for Banggood).
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGKK215, AFfbG10, BGBFRCPART, BGVDay10%off, BGMPB2020, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGRCAP10, bgshOOp10, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Here is price history (for all/most countries) for KK2.1.5 LCD RC Flight Control Board V1.17S1PRO.
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)).