If you've got just �100 you could try a weekend in Amsterdam. If you live in the UK you can get a fare for as little as �60 return on Easyjet and there's a hostel in Amsterdam which is less than �10 a night. It has a website as well at which you can book in advance, but sorry can't remember the url. Only problem is you'll probably spend at least �100 while you're there. It's money well spent, though.
For less than �70 you could go on a National Trust holiday, but you would need to work for it! Usually you help out with restoration or conservation work during the day, then accomodation is in estate cottages. The upside is you get to see some of the most beautiful parts of the countryside in a way which few other visitors ever would - hard work but well worth it for the sense of achievement alone.