Honda Odyssey Navigation! Please Help

I just bought an '02 Odyssey with navigation. I love the navigation but it is running the original disc. I went to Honda and they told me that the updated disc would run me like $250 first off, I dont want to spend that much on a disc and second, I started checking around and people are not very happy about these expensive discs even after they have purchased them. does anyone know where to get disc cheap or switch out the system and still use the in-dash screen. it is made by alpine.

~Thanks