answer:Rule of thumb if I recall correctly is $20 a month payment for every $1000 total principle. This is assuming an average interest rate (like 3–6% range). If your interest is higher, your monthly rate will be higher. If your interest is lower, your monthly rate will be lower. On my brand new car (well it’s like 10 months old now), I pay roughly $300 a month. The purchase price was roughly $17,500, and the interest rate is 0.9%. Used cars I was looking at ranged between $8000 and $12000, and my CU offered me an interest rate around 5%. My payments were going to be in the $180—$220 range.