There is a roof rack on the Mopar site:
Chrysler Pacifica Roof Rack (Part No: 82214552) It is under $400. There is an instruction page you can click on which seems to indicate that the holes are already in the van roof, so it doesn't look like you would have to drill into the roof. So you can decide if you think that would work for you.
It looks like the new Touring Plus might have a roof rack if the photos are accurate. Otherwise, you might try reading all the buying advice on the forum to get the price down on a van with a roof rack. Just try to get a manufacture date of 9/2016 or later if the better safety rating matters to you.
I got a Touring L because I wanted the roof rack but would have bought a cheaper model if it had a roof rack when I bought my van. I don't think the roof rack part was available then.
Good luck. Let us know what you think and if you install it.