Upgrading on Experience Signature 55+

Looking to upgrade an iPhone 13 Pro to iPhone 18 Pro. Must be unlocked, so I’m not looking to finance. What’s the best deal? I think the Costco $100 shop card is only available if I finance, right? Is my best option to buy direct from Apple? If I don’t select a carrier at check out but link to T-Mobile later, will I avoid the $35 activation fee?