It depends on several things. First, what filesystem type is/was it? There are plenty of tools out there that will attempt to get the files back. However if the blocks have been overwritten, partially or fully, you're looking at a lot more cash. There is a place in SD that does data recovery, they're supposed to be VERY good, and $5000-$10000 is around the price point that I recall.
Does the disk spin up? If you can get power to it and it spins, have them dupe the drive with a disk duper(you can usually get this done at a decent chop shop, I know a place in OC that can do, assuming we gave them back their duper...
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Google is your friend....