I could make a mathematical model of this, but I am not going too, because the theory should be good enough for those capable of understanding.
Premise: Buying the absolute cheapest is always the budget decision.
There are a few main ideas why we would want to pay more.
1. Pay more, and I get discount.
2. Pay more, and I get better quality, products that last longer.
3. There is something dangerous, bad, or incorrect about cheap products.
Yes, each of the three point above can be true.
However, the math worldwide turns out, more like 5 percent of the time, 1 in 20 times, the concepts above pay out.
However, if you live as minimalist, never buy anything expense, and try not to buy you will have better value and quality 95 percent of the time.
What is a good deal?
A good deal is when you feel content, happy, and feel you got a good value. This strategy above will allow a person with critical reasoning skills to be happy.
However, being that only maybe 1 in 50 people are of this nature, then a good deal is normally paying more, because the other 48 people near them are also paying more
Marketing people who truly understand the point above, people like Steve Jobs knew that people needed to pay more to be happy.
What it means to me is this, I can relax on all the math when trying to buy, and just buy the cheapest. Even when I buy poor quality, I have saved so much money with other purchases, it is inconsequential.