Chris Rosser AOS 3.5 Inch Frame Kit (Banggood, Aliexpress: Props: up to 3.5 inch, Bottom Plate: 2mm, Arm: 4 mm, Fit for Camera: 19x19mm, Mounting up front: 25.5×25.5 or 20x20mm, Top Plate: 2mm, Fit for：DJI Caddx Vista, Middle Plate: 2mm, Item Name: Chris Rosser AOS 3.5inch Frame kit, Mounting in the rear: 20x20mm, Weight: 49g (with all hardware) (the best price with coupon)).
Just check coupons out (with price alert and history). Let’s see what best price is ATM.
Aliexpress
There’re some similar (or not) items on Aliexpress
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. Well, there is one coupon available right now.
Link: Banggood product page
1. ($58.87): BGMatt2022
you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGRCParts8, Tabby20, BG1efeb0, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BG8RCToy, hoNEYbGdeAlS, BGRCT10, BGJUNEGSG9, BGToys8, BG8OFFCOUPON
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for Chris Rosser AOS 3.5 Inch Frame Kit is here. The lowest price was: $57.59.
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)).