It depends where you go but the percentages are generally the same. You don't have to take the amount they offer, you can take less. What really affects the total amount you pay back is how long you keep the loan out.
For example, my sister took $600, and it was $150 each month. So, the first month she could either pay $750 and get her title back, or $150 and continue the loan for another month. You can pay the interest each month (which is calculated based on how much you borrow) but you would still owe the total plus interest when you pay off the loan. So far as I have seen you cannot pay it down in installments...it is basically pawning your car but just the title not the actual vehicle.
With all you have going on, please think long and hard about this...they don't play and you will lose your car if you miss one payment. Could you sell your car on craigslist and buy a cheaper one that would leave with money left over? Do you have anything else of value you could part with first? Jewelry, tv, camera, game system, etc.?
Like Suz said, its a desperation move and you will have zero transportation if you lose your car. Also, check the laws in your state. In Florida you can't get title loans anymore. But Florida is a** backwards with what they do and don't choose to regulate, so your state may be different.