There is a post from a few months ago where someone mentioned that they were indexing their Discourse site with Coveo: Issue with API for indexing with Coveo.
They posted a reply in that topic that shows how Coveo is configured to index the site. It seems that the configuration is auto generated by Coveo.
Looking at it now, when using this approach, you’d need to be sure that the API requests to Discourse could be rate limited to a maximum of 1 request per second. Without a rate limit you’d risk triggering timeout errors on Discourse.
This approach could work on any of the hosting plans that allow for API access.