Costs of dogs

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Im a 21year old senior in college renting a small house with 4 other guys. I have the option to get a 7 week old housebroken rottweiler/German shepard puppy mix. Whats a ballpark on costs/problems with a puppy? We dont own a anything nice (half of us are grinding it out at 3/6 or 5/10)and of couse we have a no pet clause in our rental agreement. Would I be compleatly retarded to get one ?