IRS does offer payment plans at least for some types of tax debt. But really, if you need a car but are unable to get $6000 to obtain one, I'm not sure if you have that much better luck in the used car market, since a car would still require some thousands that you either need to have at hand, or get a loan to. If you can't get a loan for a $6000 new car, can you get a loan for a $3000 used car?