The NPC market would have to sell based on what it costs now to build a thing in order for it not to be punishing to people who don't participate in the new wood/stone/etc economy, so that there would ultimately be no change in price.
That's not necessarily true. It would just have to be balanced properly.
We have changed the balance of prices and other such things before, both deliberately and less so. We might do so again—possibly making some things cheaper, and other things more expensive.
Or, as this is all still basically spitballing ideas, we might not
