Please help - Recover jpg from corrupted Raw files

Please help if you can.

I used a card from our university check-out to shoot a wedding ceremony this week, and after working normally for about an hour, the files suddenly would not show on play back. I switched cards and shot the rest of the formal portraits, but the only photos of the ceremony are on this corrupted card.

It is a PNY 16GB SD card. I shoot with a Canon 6D. As soon as the error message started showing, no previews could be seen on the camera (up until this point, I had been reviewing images normally). When I inserted the card into my computer (Macbook Pro running El Capitan), it was unreadable. Using a USB card reader made no difference - still unreadable. I purchased Stellar Photo Recovery software ($40) to recover the files, and I was able to download them. Some of them have visible previews, but the raw files are unreadable (either color bars, black, or unopenable). I also tried some free software options (Disk Drill and one other) with no luck.

I then tried Instant JPEG From Raw to extract at least the embedded jpg files, but only a handful (4 of 83) are usable.

Is there anything else your recommend trying?

There is a Photo Recovery software from PNY that shows preview images when I perform a free scan, but I hesitate to spend another $40 only to get more unreadable corrupt files. I shot the wedding for a friend, and it was very casual, but I would hate for them to not have any images of their ceremony.