This really sounds exactly like a very common use case for using a jquery/javascript menu plugin. I think I would not go the path to roll my own solution for this. Rather invest some time to get your head around one of those frameworks (superfish is pretty easy). Maybe you find some other plugins here:
http://www.tripwiremagazine.com/2012/12/jquery-menu-plugins.html
The key point for simple-navigation is to render all the items on page load (using :expand_all => true).
If you need further help, let me know.
Andi