Latest gen iPad (not Pro). About the same price as mini which is way outdated. iOS is most stable platform for DJI. It is a little big (though that is also a bonus as well). If the mini had been updated in 2018 I would have recommended it. You can pick them up new for 299.00 not sure about used. Not the cheapest you can find, not the most expensive just like the Mavic Air. It is going to be one of the best, sorta like the Mavic Air.
Don't mess with stuff that you have to hope works or force to work, just not worth it.