I did end up helping them move their files into a Sharepoint site. They were already using a few Shrepoint sites so they were familiar with how it worked.

What I wasn't familiar with was the miserable process of migrating the data to Sharepoint. My client has a T1 connection, so uploading using any server tools was out of the question. I had to remove the data and figure out how to upload 500GB of data to Sharepoint and OneDrive. The answer: SLOWLY. It was miserable. I tried using the OneDrive sync client, but even the most recent one failed completely. It uploaded 50GB in something like 12 hours which was totally fine, but then it slowed to a crawl and would upload 5 FILES every hour. So eventually I had to go through the web interface and drag and drop stuff. But this was fraught with difficulties. It would randomly fail, the browser would freeze, and I'd keep hitting the 256 character name limit. Just a mess. Also, I had to go through and bulk rename every file that had illegal characters in them ( #, $, % ).

This was a nightmare. I'm thinking of trying to upload the same files to Google Drive and see what happens.