You and I have worlds where the prices can change with the campaign.
Actually I think everyone does, just some GMs haven't realized it.
If you've set an adventure in a gold mining camp way high in the mountains,
although you may not be aware of it you've either figured out a way food can be grown up there just as easily as down on the plains, you've figured out how to transport food up the mountain at no cost whatsoever, or you've thrown off the values in your equipment list. For a decent breakfast or a bale of hay to cost less than half a gold piece simply doesn't make any sense in such a context. 4 grams of gold is a lot easier to find on that mountaintop than ham and eggs.
To be sure, if neither you nor your players ever spot (or care about) the logical fallacy you've created in your setting, then no harm no foul.
For us it gives that bit more realism that our players maybe also expect. I guess we expect that from ourselves, as we know that prices would change to this direction then we must do it for the campaign to stay true to ourselves as GMs.
And that's my point. If you plan on selling it to RM GMs, your target market is by definition a group of detail oriented people who are likely to want to change things around the edges to make them fit the scenario better.
However I think that a rulebook needs to serve the wide audience that is happy with ready-made standard price lists. I guess thats what works for the most groups.
Sure. If there are 5 books (Characters, Arms, Spells, Creatures, Treasures) then I'd expect to find the "standard price list" in the character book. But if it's RM, and therefore can be assumed to be detailed and tweakable, I'd also expect to find a "how to build a price list" section in the Treasures book as well.
In the end the prices and currencies should not make gaming more difficult and I guess it is better to make it simpler rather than too complex.
They shouldn't
demand that your game become more complex, but they should
allow for it, otherwise you'll lose players who feel like it's "too cookie cutter", as D&D lost customers to RM when it first appeared. It's easier to simplify from an existing complexity than add complexity to something that is not only simple, but
complete in that form. Something like how if you cut a board too long, you can always make it shorter, but once it's too short it's too short forever.
If the characters in someone's scenario consist of thieves, counterfeiters, maybe a jeweler or lapidary, a few spies... I'm not gonna tell that group they're stuck with a standard price list and exchange rates will always be one to one wherever they go. They'll never go for it. To be sure, a gaming group picking up RM
for the first time is unlikely to have that kind of composition, fair enough. But when they get far enough into it to have those kinds of ideas, you don't want them to
drop RM for something else because RM is "too cookie cutter", right?