This will be unique to each witnesses set-up. The top guys will have replicas, backups, full nodes and the cost here is likely to be 3/4 times more than the 'basic' setup.
We are taking the approach that if we move up, the more kit we lease. As a back up close to the hundred, i don't think there is a need to go all out yet.
I hope your need to go all out comes sooner than your think @abh12345! 😁
Thank you, me too! :D