There is a thin but long crack (1-2 inches long) near the joint and along the back casing (the part encasing the monitor) of my sony vaio e series laptop.

Is this an easy/cheap thing to have repaired? is there an effective way to repair/prevent this from getting worse myself?

The crack is thin, nothing can get into it (except maybe water but i don't want to test that for obvious reasons...). The crack is flat when the laptop is closed, but there is an obvious raise in height of one side when opened (scratching either direction when closed (lightly of course) provides no resistance, while open a resistance can be felt in one direction but not the other)

I've been told it could just be a stress crack, from the opening and closing of the laptop, but this is why i'm a bit worried as i use my laptop very often (though i am usually on it for a great deal of time each session, so there's less opening and closing than if i were using it off and on)