Go to progressive.com and see how much an insurance payment would be. I pay 1500/yr for my 2013, and I've been driving for 15 years. Let's just say for comparison that you'd have the same rate.
That's ~$120/month, just for your insurance. (It's going to be higher than that)
Say the car you find is $12k. Probably about the middle of the range pricing. With a 3% car loan over 60 months and no money down, you're looking at $215/month.
Gas, you can expect to spend ~$0.70 per mile. give or take, based on $3.50/gal. Say you drive $300 miles per month, that's $210 just in gas.
So let's do the math so far.
Gas - $210
Payment - $215
Insurance - $150 (I rounded up)
How secure is that $700/month you make? Do you ever go out with friends for pizza and a movie? Can you afford to fix things on your car? etc. etc. see above from Jack.
Drive a 25 year old toyota like the rest of us did at 16.