You could put all the files on Google Docs, then scrape the results to your own web site.
My concern is that OCR accuracy is still an issue, so one consideration for a search requirement is the ability to perform "fuzzy" searches. Fuzzy meaning when the OCR incorrectly recognizes the word "hat" for "hot", the search engine will be smart enough to return results that are similar but not exact. In Oracle, there is a function called UTL_MATCH that compares the similarity between two strings: http://docs.oracle.com/cd/E11882_01/appdev.112/e25788/u_match.htm#ARPLS352
A function like this would be useful.