Here's the specific options:
The first choice is to Pay 25 dollars, and keep it indefinitely on your switch. And if you wish for online play, you just pay for it separately. I would think standard online should also still work here if you chose this path.
The second choice is to get an expanded switch online subscription. Along with the DLC, you'll also access Sega/N64 games as they become available - But you don't own the DLC, and must renew the subscription each year to access it.
The price for the expanded online part varies: It's 50 dollars for an individual subscription, and 80 dollars for a family plan. The family plan supports up to 8 switches, and could be manually rationed up between players to pay for it. Of course, setting something like that up might be a bit complicated.
I personally would rather just keep it simple just buy the DLC and keep indefinitely, and only pay for online when I really want it. But I'm quite curious about other people's opinions as well.