mercedes wants $1,680? i have 2004 e320 am looking to get dvd navig box where can i get that mercedes wants $1,680

if someone would be kind where can i order at lower price

Check on E-Bay. I see them there from wrecked cars often for only $500 and less. Most sellers include all the wires and even the head unit. But, MB nav systems are horrible! Save yourself some more money and get a TomTom one system and be able to use it in any vehicle you have.

Try car-part.com. It is a search engine for all the junkyards nationwide.

What's a navigation BOX? Do you mean your car doesn't have a navigation system and you want to install it? If yes, you can try to do a search on "Mercedes parts" and you'll find a lot of places selling all kinds of things including navigation.
Word of caution, unless you REALLY know what you are doing, do not install it yourself. It's not that simple. If a dealer wants $1,680 including installation, it's not a bad price...
You may also look into a portable unit. Of course, it will look a little "tacky" in your car, but some high end portable units are better than original Mercedes one (more features, easier to use and much less money.)
I compared my portable unit with the one my friend has in his Mercedes and mine is MUCH better, so I decided to leave my E320 alone and not mess with it.