$18k/yr in most major US cities probably implies:
* Subsistence diet
* Dependence on small selection of rental properties
* Extremely poor access to health care
* Dependence on informal "gratis" child care
* Near perfect job attendance
I call these out not to make the boring "gnash our teeth about the lives of the poor" case, but rather the suggest that your ability to care for a family on 18k/yr in a US metro is counterfeit: you can do it until you:
* Are ever hospitalized
* Lose your free child care
* &c ...
... at which point bang you're bankrupt. I think a lot of people who think they are getting by with low incomes are actually playing a kind of sick inverted Martingale betting strategy against life.