Have you tried it, or are you just guessing?

Yeah I've run various yolo implementations on my main computer and I've read what other people have measured on current and last gen raspberry pis.

Again I think people overestimate how much compute this takes and underestimate how cheap embedded compute has gotten.

I see on the rpi website [1] that an RPi 5 costs 120$. That's 25% of the price of the FPV drone (500$).

Then you have to integrate that RPi to the drone, both mechanically and software-wise. From YOLO, you need to actually get into commands for the autopilot. There is work involved.

And another question is: can you order millions of RPis like this? If not, what is the cost of alternatives?

Not saying it's impossible, just saying that people tend to underestimate those questions. I know it from experience, I have seen projects fail because of that.

[1]: https://www.raspberrypi.com/products/raspberry-pi-5/