$500 will get you a better aftermarket HU stand-alone, but you also have to account for the adapters. (Do you still want some of your steering wheel controls?)
Also, $500 is a lot for an RBZ. I paid $260 for mine (snipe!), and I usually see them for $360 shipped as a "Buy now" on e-bay. But maybe the price is different because your are in Germany? BTW, if you are in Germany, I'm not sure if the European version of the RBZ (it actually has a different code) works in an American JK (assuming you have an American JK).
Couple of questions first.
Do you have the Connectivity package?
Do you have the Alpine system?
If you don't have those options, go aftermarket.