What’s the range like on the Aio? It seems like you would need at least 900 feet for a fixed wing.
Range is a function of transmit power, receiver sensitivity, antenna gain, and a few other things... so I will give you my experiences and let you make your on choices.
I have FPVed quite a few craft with a 25mW AiO with a RHP circular polarized antenna on it with some lower end box goggles (I am looking at upgrading, but with going to FF, thinking about waiting to see the vendors there) with diversity with a omni-directional and a patch antenna on it. looking at the field I was flying at, I was staying roughly in a 600ft 1/2 bubble around the flight line, including flying behind some trees. With this I got a few static moments, but nothing that was a big deal. I have since upgraded to a higher end device and am running 100mW and getting basically 0 issues.
If I wanted to get more distance, I could get/make a better directional antenna, but then I would have to make sure it was aimed at the plane. I will say for the size planes I was flying, don't think I would need more then 100-200mW TX power to cover anything that could be considered in LOS.
There are also AiO's that can go up to 400mWs, so if you go on the high end of them, you can definitely get enough power to cover you.
If your really sure you want to get into this, it wouldn't be unreasonble to expect to spend $500+ even for Analog to get a good set of goggles + a reasonable camera/VTX.