Data matching software

Hi, I am wating to discuss with companies a serious opportunity to develop a piece of software that will be used for data cleansing... ie: Take a large database of business data, approximately 4 million records and run against it files/client data of maybe 100,000 records and analyse all fields against the master database. On completion a report will be created detailing all the differences between the master and the client data. This will be a large project and I am looking for a company that will come on board with the entire application and create it start to finish. Regards, Ian