The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money.

Take boots, for example. He earned thirty-eight dollars a month plus allowances. A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. Those were the kind of boots Vimes always bought, and wore until the soles were so thin that he could tell where he was in Ankh-Morpork on a foggy night by the feel of the cobbles.

But the thing was that good boots lasted for years and years. A man who could afford fifty dollars had a pair of boots that’d still be keeping his feet dry in ten years’ time, while the poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet.

GNU Terry Pratchett, from "Men at Arms"

Let's look at the new average cost of a car. Roughly 50k. The average loan amount for new cars is right over 40k. (Meaning they are paying 20% upfront by either trade-ins or down payments. The average car loan interest and length are 6.84% at around 67 months.

So that would mean the average person pays $8,235 more than a rich person.

So it really makes out to be that there is a 120% charge on the 40k they borrowed.

Note: car insurance costs are based off the area you reside in, and your credit score. So you will pay more to have it as well.

Poor people pay more on everything. And when you compare how much money someone makes it isn't direct like many people view it.
Someone who makes 40k vs 50k isn't a "well they don't make that much more"

If the cost of living in the area is 35 a year. One has $13.69 /day spending money. The other has $41.07 /day spending money. $178/day if you made 100k in that area.

So someone making 40k if they spent money on nothing else, could buy that car outright in 10 years... 100k doing the same could buy it in October, of that same year (271ish days)

Drastically different living/saving possibilities between them.