The firm I'm working at uses IRIS. Not sure how much it costs but they have it on every desktop.
Essentially, it gives the user a search bar which allows them to search documents anywhere on their computer. It searches through PDF files, which is why they bought it.
They scan every document about a case into a pre-arranged directory structure. When somebody needs information that isn't in our database, they can just type in a defendant name or case details into their search bar which will scan every PDF document in our case directories. All files are indexed so the search is pretty fast.
I was looking at Google's desktop search tool and an addon referenced on their web site but it wasn't doing it for me.
Please let us know what you decide and how you solve the problem.