To answer your original post question you can submit online and it gives you a single and multisiged item price.
You list the primary (or most valuable) Dimaggio and Gehrig respectively to get the price but they authenticate all of them.
Here is a screenshot of the results of Gehrig with 6 total sigs for encapsulation ($350) and a link to the page I'm referring too.
https://www.psacard.com/services/autographencapsulation
Awesome pieces!
Sent from my SM-G960U using Tapatalk