You made me remember that the server sits idle most of the day: if they are 5 persons doing 100 queries per day where each query takes less than 1 second, the server will be fully busy, all cpu core maxed out, 500 seconds per day that means there is still 85900 seconds available (~23.86 hours) on all CPU cores...
What if the server provides more "services" or "applications" like #NextCloud? Would 10€ per month per users makes sense?
The features only of the search engine part: https://etherpad.wikimedia.org/p/babelia
At that does not include taking into account user feedback to be able to program the crawl from the search e.g. via a feed reader.
Also it does not mention interop between search engines which we dive in https://etherpad.wikimedia.org/p/peacesearch
For people who care about, support, or build Free, Libre, and Open Source Software (FLOSS).