There should be a shop in the lounge where you can buy diamonds for 300 meebles each from the donator lounge. That's 200 meebles off the admin shop price. You could also put lapis lazuli for 5 meebles each.
This way, donators would have better stuff, therefore enhanced gameplay. Better tools, and better armor.
And by giving ranked donators this advantage, more people would donate to the server to get a rank.
This money would help keep the server running, and let you do more events and updates.