No clue what you're talking about - Ubuntu, like most LINUX distributions, is free and the updates are also free.
There is no "maintainance" that is very high on it.
Because monitoring 100 rigs on Ubuntu with no monitoring solution is very high maintenance.
use a windows PC/laptop with the right monitoring software then run the rigs with ubuntu it's actually is better easy to work with etc and the drivers for Ubuntu 15 and lower add monitoring any way .
What software let you put a preflashed OS on 500 rigs and control everything from a single file, with no need to connect to individual rigs?