After some basic googling and read of the EULA I shall present to you a few ideas.
Idea number 1 - Meep Merch:
Meep Merch is a great idea and is bound to make the server some money. What would be a lovely add on is if someone bought a t-shirt from meep that they get a lovely FREE code that gives them some in game perks and unlocks a lovely title *hinthint*. As long as the meep merch has no affiliation with minecraft if would be meeps own brand and therefore the rank would not be bought. You aren't making money off of minecraft (simply making money off of meeps brand) and therefore it is in accordance with the EULA.
Summarised:
Play buys merch, merch comes with a code, player puts code into meep, player gets a lovely treat.
Idea found at: https://www.spigotmc.org/threads/store-method-bypassing-eula.21270/
Idea number 2 - Buying all the perks:
Why not have the option to simply buy perks using in game money, therefore all perks are available to all ranks. However the higher up the ranks the higher the level of discount on in game perks (VIP 10, Premium 20, Exclusive 30, Elite 50, Supreme 70, Ultimate 90 ?) this would mean that no one would have an advantage as all perks would be available to everyone.
Summarised:
Discount on perks for higher ranks
Idea found at: my brain
Idea number 3 - Seperate worlds for seperate ranks:
I'm not 100% sure if I like this idea but it's worth putting it out there incase anyone else has ideas on how to adapt it. Essentially different ranks would have different servers (whitelisted when ranks are bought) these servers would have all the perks as were previously set.
Summarised:
Different ranks have different servers
Idea found at: my brain (although I'm sure others have thought of it)
Thanks for reading
Also please add any more ideas which I will then add to this list. We all want to help staff and the server out and totally not just get good perks for ourselves.