What car would honestly be best buying?

I was just offered a job at a pizza place working 60 hrs a week. The car I will be using will drive 100 miles per day, 30 days a month. What car should I be considering buying for this kind of driving? I am not a gear head, a car newbie. I only want this job to last til September. I will be making $700-$1000 a week. Is this any worth it? I have a 2008 Mustang GT sitting in the driveway but I don't want to get involved with 3k a month mileage depreciation. I want to work a week with the Mustang and use the money I make for a down payment.