I think you've made a mess of the problem. First of all, as I've said before... or maybe I haven't. Maybe I was talking to myself or something.
Anyway, the first thing you've got all wrong is this: FOOD! Is there just some type of generic food that costs the same all the time? Gruel? sloppy joes? Marshmallows with fudge? What is it? There should be multiple types of food with different costs, which brings me to my second point...
Who cares if the costs are the same from system to system! Make up your own costs for the things! Maybe money in warhammer is a bit easier to get than in myth, making one golden crown worth more in myth than in warhammer. It's never always the same. Ya gotta see these things, FFFFRRRRREEEEEDDDDDOOOOOOoMMMMMMmmmMMmm!
