I would suggest a variation of the following as a way to get some quick cash:
Focus groups (I'm doing one on Tuesday that pays $150 for an hour and a half)
Mystery Shopping (again, I'm doing three next week. It's free food/gas/item for a convience store plus about $50 total)
Sell plasma (I passed that phase about 15 years ago)
Offer to do odd jobs around other people's homes (my 14 year old is doing that @ $8 an hour, put an ad on craigslist)
Sell what you have or have a garage sale
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Any combo of the above will net you quick cash but seriously put some thought to letting the car be repo'ed (or sell it if you can make ANY amount of money on it, including one dolllar). Then save the monthly payment and buy a car. You can also save a tremendous amount of money by tweaking your food for the month - make lots of lentil soups, rice, and use up every bit of leftovers in your pantry.
The last thing you need to do is borrow more money and dig deeper. Try and make do with what you have currently or less - if you work your budget you can survive on way less than you likely think. Do you have cable?
Good luck!