Credit cards and payday loans support all purchases and actually exacerbate this issue by extracting money from people. It makes sense after all, they are a service that has to make money and if rich people don't need their service, where is the money going to come from?
Affirm could work if it was not trying to make a profit (maybe off VC funds), but it is difficult for me to understand how it will solve this issue and be profitable.
The problems for the poor in modern America are health care, education, and rent.
Literature doesn’t have to write literally about something for the point to be made. The boots are a stand in for whatever the issue at hand IS (rent vice buying a house would be apt).
Health care: you can afford your insulin or you blood sugar goes out of whack and you end up in the ER.
Education: you can't afford the time to learn a new skill (or even attend school) so you can't move up out of your low-paying job.
Rent: you're paying high rent instead of owning.
The issues extend from these all the way down to the boots level.
Now. But in the past it was plausible. See this list of assorted wages and prices for items in the mid-19th century in the US [1].
Boots were around $25. There were many jobs that paid low enough that $25 would be in the neighborhood of 1.5 months worth of pay.
[1] http://anotherandrosphereblog.blogspot.com/2013/03/how-much-...
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 a 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. This was the Captain Samuel Vimes "Boots" theory of socioeconomic unfairness.
-Sir Terry Pratchett
https://en.m.wikipedia.org/wiki/Boots_theory