That almost never works for the reason you describe. For any quality item that lasts M times as long as the cheap item, you can almost always find N > M such that you can buy N copies of the cheap item for the price of one quality item. You do not spend less in the long run, though you can convince yourself of that. The primary effect of buying cheap is not financial, it's that you're dealing with less quality over the entire usage lifetime (hence getting less utility out of it) and the replacement effort has cost (but which for poor people is very little by definition).