if you worry so much about the cost, maybe you shouldn't buy a porsche. Or maybe, you try to figure out what cost what so you don't get ripped off by your dealer.

Anyway, I can get a new battery (for mercedes E class) for the price of your wipers

You should never get a new battery from a dealer. There are plenty of shops to get them for half the price. Tires are the same. There are usually way more expensive at dealers. Basically, all you should do at a dealer is maintenance. For everything else, it will be cheaper else where but you loose the convenience of just dropping the car for maintenance and get everything done at once.

Good luck. BTW, when do you get your car, I kinda forgot