This is where Linux is really good, you can take a raw image of what's on the SD card using the dd command. Once you've got that, you can experiment with the original card in the knowledge that if you make things worse, you can restore the original image and try something different. You might even be able to mount the image using a loopback device and attempt to clean it up without having to touch the original. There's a reasonable chance that the image data is still there, you've just managed to trash most of the directory pointing at it. If it was a clean card to start with, there's even a sporting chance that the files are stored sequentially and you can recover them with a bit of raw sector manipulation using the dd command.
If you can get a PC, try to also have a Linux LiveCD to boot from.