How much can I spend on a car?

Im a recent masters graduate and have been job searching for a couple months and finally found a job offering a salary of 75k. I need to buy a car to commute to work, with ~$15 of bridge tolls everyday. My student loan payments are around $750 per month and I want to give my parents $100-200 per month because I live with them. With $15k saved up, how much money should I be willing to spend on the down-payment of a car, and how much monthly? I also need to figure out how much money to start putting into retirement plans, investments, savings and such.