What is the cost of EasyDuplicateFinder?
Based on the information on the official website, it appears that the software is listed as 39.95$ while the MSRP price is the standard of 59.99 $ as seen for most applications. However, I wouldn't rush to buy it. There is the possibility to test it. Download the available package and use it with your data to see if it's capable to do what it says otherwise it might be difficult to obtain refunds.
Note: Make sure that you also have an antivirus installed, just to be safe when installing apps.