This is a little bit of a variation on what you asked, so if isn't something you can consider doing, sorry not to be very helpful. :/
But, if you have room in your budget for a short term payment, it might be worth considering buying NEW. You can shop for a bare bones 2012 model. This is actually one of the best times of the year for doing it. You buy this/last year's model brand new. The dealers are looking to get rid of them, because the model year is over and the 2013's need room on their lots.
When you combine that with the fact that used vehicle pricing is ridiculously high b/c of the cash for clunkers, and the economy forcing people to buy used and not new, and holding onto older vehicles longer.... it really makes used cars in demand and raises the prices on them.
The bonus with buying an older model year (2012 still on a lot) new, is that it IS new. Full warranty. No miles.
Seriously. You should check into it if you have room in your budget. I am NOT one to advocate signing up for a car payment. But, I also am not one to spend a big chunk of $ ($6,000) on a big fat question mark. And when you buy used, no matter WHAT they tell you... you just don't know when the big ticket repairs are going to be calling your name.
New tires. New brakes. Transmission. Clutch. Starter. O2 sensor. You just don't know... it could be SEVERAL of them over the next 20 months.... and you could (theoretically) be half paid off on a brand new car during the same 20 months... and NO repair issues except general regular maintenance.
So... just another way to look at the big picture.