Beam width -3dB at +/- 45 degrees (H + V) (90 degree total), 8dBi gain, 5.8GHz ISM Band, Weight 7g, Impedance 50 ohms, F/B Ratio >356dB, VSWR < 1: 1.35 at 5800MHz. 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. ($9.22): BGTT10
2. ($9.22): bGhOnEy10
3. ($9.24): 13f142
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): bgshOOp10
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for ImmersionRC Mini Patch 5.8GHz LHCP FPV Antenna is here. The lowest price was: $5.99.
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)).