Well, one way to work the market idea, is to go the same route as Mad Max, or a number of other post-apocalyptic media. The collapse was less than total, and there are still bastions of humanity - though manufacturing is quite limited, as might some other technologies like electricity, mineral extraction etc.

The classic "Adventure Towns" and "Wandering the Wastes" tropes if you will.

As such, there is still a need for independents to search the wastes for supplies. Caravan guards, would be another popular occupation - though raider a bit less so with the zombies about. Perhaps they have all the goods/money they need, but the items they want are only in a very remote location.

One idea I had for running a long term zombie game, was to avoid the classic pandemic. My players got stuck on an oil rig, dealt with the zombies, and picked up clues that someone infected the other workers intentionally. Hence the world at large knows little and is uninfected, but there is some conspiracy that is testing reanimates. (and they're far more careful than Umbrella I might add) Every few games its new creatures, as they're investigating low scale weapon tests, along with the how and the why. When they finally confront Mr. Kube, the whole series gets turned on its head...
There is a fine line between hobby and obsession. I seem to have lost sight of it some time ago.