I've just been looking for Zandvoort TDs and found these:
http://www.motorsportlifestyle.nl/dataenprijzen.asp
5 x 20 min sessions so a reasonable amount of time on track but nothing amazing.
Having had a look you'd want to be in group 3 or 4 to be able to ride freely round the track, in group two you follow instructors in the morning with the choice to follow them or lap freely in the afternoon, group 1 is behind instructors all the time. But I'd check over the phone first as this is just decrypted from a beblfish translation!
Quite a few monday sessions which could be handy for tagging on to the end of a trip to the Ring/euro tour. Zandvoort is about 20-30 mins from the port of Ijmuiden (Newcastle-Amsterdam route), so you could miss your last session, or may strike it lucky with timings and still make the ferry! Alternatively it's about 1 to 1-1/2hrs from Rotterdam Europort.
If anyone books up on one let me know (or possibly wants somewhere to stay), as I'll be going to a few of these given it's only 3 miles from my door.