M20 is now available on official website within your budget.
Running a usb cable on top of your helmet for charging may not be a nice idea.
Are you going to use this for Motorcycle Rides?
I am using Sony HDR AS 100.
Microsoft wireless display adapter can give you a reliable range up to 23 Feet (According to the manufacturer).
As per my understanding this device supports uptp 1080 p resolution.
https://www.microsoft.com/accessories/en-us/products/adapters/wireless-display-adapter-2/p3q-00001
U2412M User here. Decent panel. However this is an old model with USB2. Getting this one in 2016 is not a great idea. There was no issue with display in couple of years. I might sell this to get a 4K panel.