I have just checked coupons. The lowest price I could get is $16.99 for 150mm Triple Feed Patch 5.8GHz 14dBi FPV Antenna (in Banggood). Price history, coupons and price alert are available on this page. Do you want to know what the best price is?
Center frequency: 5.8 GHz, Radiation efficiency: 75%, Axial ratio: 1.05(0.38dB), Antenna gain: 14.4 dBi, Matching: S11 < -30 dB / VSWR < 1.065, Half power beam width: 30° (horizontal and vertical), Bandwidth: 660 MHz (5.47 – 6.13 GHz)
Latest coupon and price update (UTC):
Banggood ($16.99)
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. Price? Pretty sweet, this is the lowest price I have ever noted for this product!
Link: Banggood product page
Price: $16.99
This is the best price ever noted in my database!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): Parts8, BGJON8, BGRCParts8, Tabby20, BG1efeb0, 8Couponsde, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BG8RCToy, BGRCT10, BGf610c0, BGJUNEGSG9, BG8ReviTrage, Cuponation9, BGToys8
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
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
Here is price history (for all/most countries) for 150mm Triple Feed Patch 5.8GHz 14dBi FPV Antenna.
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)).