Wow, I'm surprised to see so many people trying to dissuade you from Amsterdam. It's a great city for a party, even without the sex and drugs
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You can eat in any price range and there are loads of bars and restaurants who would love to host a party for 20. We are in an economic crisis after all. If I were you I would not plan too much ahead. Just spend the first night in city center enjoying a few drinks and scout around. There are loads of fun places. As you walk out of the Centraal station, to your left is the red light district which you would probably want to avoid. Instead head slightly to the right of center and you will see lots of nice places.