Thinking about this a little more abstractly...
We could model the availability/redundancy/quality of goods and services according to Maslow's hierarchy
https://en.wikipedia.org/wiki/Maslow...archy_of_needs
Purveyors of food/water/shelter are common and plentiful, even small outlying communities could regularly provide some excess for sale.
As you climb through security, psychological and prestige tiers things that support those goals become rarer and more expensive, perhaps only being available at certain times or in specific locations.