The mistake I see made by people all the time with adverse credit is that they think they can only get a few thousand dollars so they will look for a car and then go and get approved for finance. WRONG.
WARNING: If you read this website, your chances of getting car finance with bad credit will dramatically improve.
Speak to a lender or a broker and they will be able to get you approved based on what you can afford to repay. You will be surprised at how much you can actually borrow. A lender would also rather lend you a bit more money so you are able to get a better car. A newer car is more reliable and is going to give you less trouble. Because of this, you wont have to be spending money to get the car repaired and therefore it will not have any impact on your ability to repay the loan.
Also, if you do have adverse credit and you are able to get your life and finances sorted out again, what a reward to be driving around in a brand new car. But hold on, I'm not suggesting you going to be given $40,000 to go and buy a new car, more often than not, you might be able to get $20-$25,000 which can buy you the ever popular Mazda 3 in any colour you want.
When you are buying an older car you are often doing this from a car dealer, there margin that they need to make often is as much as what they paid for the car themselves and financiers are aware of this.
Some lenders will only lend to you if you buy from a car dealer, obviously meaning you can buy either new or used. However if you wish to buy a car privately, the number of lenders you have access to is dramatically reduced, meaning what you save on a car buying privately, may end up costing you more over the term of the loan in higher interest repayments.
Speak to a broker or a lender and they will be able to tell you how much you can borrow first, then you can go car shopping looking for a car you can afford.