Ivan Wilzig, the eccentric banking heir and musician, is cutting the guest list to his over-the-top parties by asking people to pay. Wilzig has ruled future guests must make a $200 donation to his Peaceman Foundation, and he’s already raised $20,000. He’s planning smaller events at his Water Mill castle in the Hamptons instead of the annual huge summer bash, which has often ended in some wild revelry. “I want to make the castle the Studio 54 of philanthropy,” Wilzig announced to Page Six. “At the very big parties, it’s hard for me to say hi to everyone.” No press will be allowed — to let him get to know donors “on a more intimate level” (ahem). This weekend, Wilzig is throwing a party and giving guests access to all castle rooms. He says the fee is cheap for most Hamptonites and compared to “inflated bottles and nightclubs, it’s nothing.” Wilzig will also throw parties at his 2,400-square-foot Soho penthouse painted with flowers, rainbows and peace signs. “The entire space is black-lit,” he says. “It’s a psychedelic love shack.”