Ending my in house employment, they won’t buy a drive for file storage - any tips?!

Hi all, I’ll try and keep this brief. This is California, dealing with a semi-large company of more than 25 employees.

I’m leaving my position as an in house videographer for a mid size education institution.

Up until this point, I’ve always worked remote other than shoot days, and have provided all the storage media for the files and videos created for them. I work freelance for other clients, so I treated their files like anyone else’s on my home drives.

I am now leaving my position to become completely freelance, and have requested they purchase adequate storage media to store the files. My contract says that all files shot on the clock for them are owned by them, and I need to hand them over before I leave. They want me to upload it to their cloud servers from home.

Upload just isn’t realistic for 5TB+ of raw video files for many reasons, not to mention I don’t have an infinite WiFi plan, so uploading those files will throttle my connection and add costs at the end of the month.

What are my options here? My plan is to continue asking for a drive until my final day of employment, and then purchase my own drive, transfer everything to it and invoice them for my time and the drive.

My worry is that because the files are technically theirs, can i “ransom” the files like this if they don’t purchase the drive during my employment? They’re not providing a realistic option for transfer, and I’m concerned I may get in trouble for not transferring their property before I leave, like my contract says I must.