Thanks for the reply. It was an old Western Digital HDD. I got the data retrieved for less than $350, and that included the cost of a brand new hard drive.
I learned a valuable lesson about backing up data frequently, at a cost that turned out to be much lower than I feared it would be. Remember folks, backup your data now if you haven't recently!
If anyone runs into the same problem that I had, here's a place I would recommend:
https://www.icubedev.com/