First i will say,
You can get a good radio, mp3, etc player for a car for 300 bucks or less.
For the DVD player, your best bet is to not use this in the dash, the unit's like the BOSS, laser, and other cheap branded radio's suffer from the same issues, the decks get hot, the screens warp and the systems break yearly. My buddy has had three of these in 3 years, that is roughly 900 bucks, which at 900 bucks you can get a nice pioneer or kenwood deck that would have standed the test of time to begin with. Navigation, get a tom-tom or a garman, yeah in dash is nice, tom-tom has free updates, the indash typically you have to pay for the dvd updates to be sent to you. Also depending on where you live, these units are major targets to theft. So get an alarm prior to this... If you can, just get the visor vanity tft screens and run them off of a secondary dvd player, ps2, or xbox360. I had that setup in a corolla, and never had an issue with theft. also if something breaks they are not all in one unit, because lord knows that driving listening to the wind for 8 hours is worse then having once tft screen break.