iBook - Help, my screen is on acid!

I have an iBook G3 500 MHz. I bought it in 2001 or 2002. I can't really use it anymore because the screen is all blurry and the colors are way off. It's fine for 5 minutes after I turn it on, but then it gets blurry and stays that way.

My questions are:
-what's the problem?
-should I bother having it repaired (it's an old machine) or should I simply sell it to someone who buys broken laptops?
-how much is it worth? Everything works fine aside from the screen.

Many thanks!