The lens assembly might just be dirty (dust, maybe a piece of hair). You could try to clean that off yourself. Others here have more experience with that. You might be able to do it without taking anything apart (personally, I'd open the disc tray and blow into the opening with compressed air, a fan, or a hairdryer). You could take the top off and probably find the lens pretty easily.
If you really like the player, and that doesn't fix it, then service is an option. For a $100 player, though, I think that you'd be a lot better off just buying a new one. Having it serviced could cost you a lot more than that.
EDIT: I just saw your other thread where you want to sell it and mention that you're going to try to clean it.