External Drive Invalid B tree Node size error

Overtime I plug 1TB WD Elements External HDD to my MacBook Pro it gives me back this error - “The disk you inserted was not readable by this computer.” The same error result I received on my friends iMac. Verifying the hard drive gives me another error named ‘Invalid B-tree node size' 'This volume could not be verified completely' and 'Error: This disk needs to be repaired.

After a session of repair it seems like not fixing the problem and giving me the message ‘Disk Utility can't repair this disk.. disk, and restore your backed-up files.’ Do I have to pay to get this hard drive work somehow. Any idea how much will be the cost of fixing it?