Advanced but cheap

Skydroid M1 : https://www.aliexpress.com/i/4000179012444.html

Skydroid Manual : https://www.foxtechfpv.com/product/radio-control/T12/190618-T12-manual-en.pdf

Video manual : https://www.youtube.com/watch?v=qOEpxxcQumk

Skydroid Switch Board : http://www.skydroid.xin/media/20200716174249ty.pdf

Skydroid AV Conversion Board : http://www.skydroid.xin/media/20200716174305Zi.pdf