We will de-duplicate your existing data in Salesforce by finding duplicates based on criteria that makes sense to you. For example matching on name, phone, email, and address. We can use apps like
Demand Tools,
Data.com, or Cloudingo. These apps have extra license costs. It is difficult to estimate hours for this task because
it largely depends on your data. Also, if you need serious data cleansing we can do that as well, but again, it is very hard to estimate hours before diving into the data.