I found a new prison server that is trying to stay fair. It is non P2W and it is not OP so the progression feels more balanced.
The big thing here is the Wardens Lair. It is a huge cave system with mobs and when you beat them they drop cash. If you explore deeper you can find hidden dungeons and get unique loot and valuable rewards.
If you like the classic prison style it also has a mine and grind progression path. There are dozens of custom enchants and they run regular community events so it does not feel dead.
