I have a cheap wifi dongle on my downstairs desktop and get about 200 mbits file transfer on my Asus AC1200G+. It is a realtek 1200 mbps £12.99 dongle and seems sufficient. Looking at a few reviews online 2 reviews rated the Asus USB-AC56 dongle as the best with speeds of 400 mbits at 9 feet. But even second hand it runs around £30 and new I have seen £60. You can get a decent router for that why so expensive?