H Annie, there is a fine I'm not sure how much - however you could be banned from entry into the whole shengen area
Obviously, this would be for repeat/gross offences I'd have thought. Ive just just and pasted the paragraph below from what looks like an Eu web site. The point made is don't Overstay!!
To many, the 90 days period per 6 months seems like enough time to spend in the Schengen Zone. Others get granted with visas that have a shorter duration of stay, like five days or two weeks etc. Still, once the end of the visa validity approaches, many of the Schengen visa holders are tempted to stay for longer, time after time asking themselves: What happens if I overstay my Schengen Visa?
If you are being tempted to do such thing, you should just know the following things:
First thing that you should know, is that an overstayed visa never goes unnoticed. The immigration authorities have registered in their databases every person that enters and leaves the Schengen, and every overstaying, even just for a day, is recorded.
Secondly, intentional or unintentional, no overstaying is left unpunished. It could be a fine, immediate deportation or even getting banned from entering the Schengen Zone for a specific amount of time.
Stu