In the Merchant of Venice, Shylock is a cold, uncaring, cruel person. All he cares about is himself and his money. He does not care about the well being of anyone else. Shylock has many cruel and heartless characteristics. They can be seen in the way that he interacts with other characters throughout the play. A ducat's worth in Shakespeare's day was about $2. So you can see 3000 ducats were worth $6000 !

To add to Jura's description, a "shylock" is a slang term still in use to describe someone who lends money at high interest and will do anything, including physical violence, to get the money back. It comes from this play, of course.

Ducats was a gold coin used in various countries in Shakespear's time. I don't think they are around any more. In that time, three thousand ducats was a considerable amount. However "ducats" is still used as a slang term for money in general.