Reach out to an attestor and discuss with them what the process is for them to trust you.
>How much will it cost?
It will likely be free. If not it will be significantly less than the cost of writing an OS.
>This presents enormous barriers of entry to both hardware and software entrants
Hopefully they are high enough that fly by night malicious actors do not bother with trying to get their insecure hardware and software to be trusted, but row low enough that good actors can prove that they can be trusted.