I am a GM looking for a narrative explanation for the wand creation costs (and by extension other simple magic items: Potions, Scrolls, etc).
I know the RAW formula (375 gp × the level of the spell × the level of the caster) and it makes sense from a game balance / mechanics POV. However, I'm really getting hung up on why this makes sense on a "realistic" level.
I am a 5th level Wizard. I have just learned the Fireball spell. I am very excited by this and I want to make a wand so I can burn all the things. I gather the materials: a rough wooden baton to be carved into an appropriately awesome shape, 50 balls of bat guano and sulfur, and my new knowledge of the arcane art of exploding fire. This will cost me (375 x 3 x 5) or 5,625gp (that's some expensive guano, but nevermind for now) and 11+ days of crafting. I now have a wand of fireball that will do 5d6 damage at a range of 600ft. Let's set the world on fire.
I am a wizened, crotchety 10th level Wizard. I've known the Fireball spell for years. I have perfected it - I cast it with barely a thought these days. My last wand ran out, so I begrudgingly sit down to make a new one. I gather the (presumably) same materials and my superior understanding of the arcane arts and it costs me (375 x 3 x 10) or 11,250gp and 22.5 days of crafting. I am more knowledgeable, I am using the same materials but it costs me twice as much and takes me twice as long as it did when I was 5th level. The spell does twice as much damage, but this is a result of my long hours of study. It has cost me years of carefully collected arcane secrets, but this is a sunk cost and surely I should reap the fruits of this labor. [Ok, I can decrease the crafting time by rushing +5 DC, which is easily offset by my awesome spellcraft skill, but still...]
I get that it would unbalance the game and remove almost all incentive for spell casters to go adventuring versus just setting up a wand shop and watching the gold roll in. However, if anyone can give me another way to explain it to my players other than, "that's just the way it is", I would greatly appreciate it.