You're not getting from Holland to Japan with just 600 euros
Heck, I don't even think you can pay the ticket with that.
It's quite expensive to fly from Holland (Damn you, ever increasing taxes!), but you should book a flight at the specialized agencies for Japan, i.e. Tozai (in Amsterdam, behind the Paleis op de Dam), of
http://www.shiranai.nl/site/ . That is a lot cheaper than through the larger agencies, i.e. D-reizen.
For good info about travel and costs, Shiranai Travel is probably the best option as it's founded by animanga fans who organize group travels (to get discount on tickets).