I'm a novice photographer and have used my Powershot A80 for a couple of years. I notice that lately when I turn it on, the LCD has a darkened background with fuschia and purple vertical streaks. This seems to go away after a while. The image on the LCD also seems jittery, although the image through the viewfinder seems fine. The pictures seem to come out fine too. Can anyone tell me if I'm about to have a significant problem with my camera, what the problem is, and how much it's going to cost me to fix it?

I did a quick research on your camera and for the price of a new one of the same make and model (if you can find a new one in that model you have; as new ones come out the price of them becomes a lot cheaper and has more features built-in than that of its predecessors), and found out that the Powershot series ( I have the Powershot A630; and lover it!) model A80 like the one you have has a street value of about $110, and for that price you are better off; if you camera is out of warranty, to seriously consider a new(er) model; like the Powershot A630.
All the LCD screen does, and acts like, a glorified viewfinder. From my experience with fixing my old Canon AE-1 Program 35mm film camera, since I cannot find that model anymore I opted to fix it about 10 years back. That camera was worth fixing, but your digital LCD display (part) on that camera; and the labor to install it; would probable cost you half the price, if not more, for a newer model with more features! :(

Since your photos seem to come out well, I would suspect your LCD screen. I have no idea what it would cost to replace the screen, but like the above poster said it probably wouldn't be cost effective to have it fixed. Unfortunately we've grown into a disposable society and most stuff just isn't made to last anymore.

That being said, if you are still getting the photos you want from the camera it doesn't hurt to shoot without the screen although it makes things more difficult not being able to read the histogram.

A new A590 IS, a far superior camera in the same family as yours, goes for about $150 new, a bargain IMO. Good luck with your decisions.