I propose Envision deactivate all non-paying accounts after the fortress has been killed.
When the player attempts to log in, offer them the opportunity to purchase funds, or charge them 10k cr to play on that world for 30 days.
Another option is to open up new servers with either 100% "free to play" (deactivate any and all options to use funds) or 100% pay to play. 100% P2P will drain your account 10000 CR / month to play on that world, which would grant you a base line 300 CP / 1 Day RT / 4 Pkg, but anyone could spend more.