Excel2002 : "Unable to read file."

Hi,

I have a few files, which seem to have corrupted due to some unknown reason. When I am now accessing them, an error pops up "Unable to read file" thrice after which excel shows some recovered/repaired data of the file. But there is lot more to the files, than what it is able to recover.

Is there any good tool to recover corrupted files?
Possibly a freeware or cheaper!

I have tried using several demo versions of tools like: Excelfix, R-Excel, Recovery for Excel.. but i m not getting full results, and these are expensive.

Kindly assist.

Thanks,
Ash.