Getting a car with really bad credit?

So my boss is going to help me get my license, because they want me at some point to be able to take her child out at least one a week. I'm a nanny, btw.

I'd be using their car while I work on getting my own. The problem is I have debts… And a credit score of 531…
I'm looking at the nissan versa which is about 12,000. I'm thinking of going into the dealer when I have 3,000 for a down payment.

My former boss' husband works in finance and has agreed to go with me because he'll know what to negotiate. I'd be able to afford around 300 a month. Is that possible? Or do you think they'll just say no?

Also toyota or honda more likely to approve me or are they all the same? Thanks in advance!
Added (1). I'm going to work on making payments on collections accounts so I have a better chance
Added (2). I will be transporting a toddler in my car. I need a reliable and safe car and I refuse to spend 3000 of the money I work so hard to earn on a car that might break down a few days later. I do not have the knowledge or the money to deal with that. I need a car that won't give me issues for a few years. I NEED A CAR FOR WORK AND SCHOOL. I don't want a car just to have one. Paying a car on time monthly is a good way to help my credit.

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