Best software to recover video files on reformatted SD and CF Cards? Or worth seeking professional help?

Hi all,

The person I work for has mistakenly re-formatted a collection of SD and CF cards (incl. Sony F3, AJA Ki Pro Mini). He needs to recover video files.

Is it worth it to have the cards professionally recovered at a place like Tekserve, or is there a software program anybody here has had success with? There seems to be a lot of recovery software out there and it's hard to tell what's trustworthy. I should mention that the software doesn't have to be free, it just has to be effective and cheaper than a professional recovery.

A few other stray but important questions:

-What are the risks of running a recovery program that fails? In other words is it possible for software to damage the old data so that no other program has a chance of successfully recovering it?

-Most importantly: is it possible to recover at least some data from a card that has been reformatted and then recorded over a bit, but not all the way? I have read that if the whole card has been recorded over, the old data is irretrievable. But there's only a little bit of new material on this card.

Thanks!