Go to Comcast's support, and see if they offer IMAP or Exchange accounts, instead of POP3. Either of the first two account types allow the creation and use of folders across all devices and computers.
POP3 accounts only allow the downloading and deleting of emails from the server. Because of this only local folders can be created an maintained. That means if you do find a Mail app that will create local folded on the iPad, they will not be in sync with your computer. What ends up in each folder will depend entirely on what you do on each device/computer.
Unless you can chance account types. Both IMAP and Exchange create folders on the server, which allows them to be synced on all devices and computers.
Another possibility to is to create a Google account and use it to access your Comcast account. A Google account can both receive and send emails on through your Comcast account. I would not recommend this as a permanent solution, but it is a pretty good way to transition accounts, so that you don't miss anything. There are instructions somewhere in Google's help pages. If you have trouble finding it (supposing you want to do it) let me know. I've found them before. The only question is, why oh why did I not save the links?