Pardon the long post. It meanders a bit.
Of course Dungeon Masters aren't entirely oblivious to the general impact of the characters' wealth.
But from a playability standpoint our analysis does not really need to get any deeper than the 1500 gp plate mail.
Why? Because the DMs that are worried a couple of mid-levels will destroy the town economy will choose a suitably low wealth curve; while DMs that don't care about that might go for the Pathfinder curve.
We can't and don't need to worry about it. All we need to worry about is price relative to other item prices. (This is not a law of nature; it's a voluntary restriction to keep this project from ballooning way out of control)
I should clarify: I wasn't talking about general economic pressures within the city/country/whatever, I was talking about competition with every other possible item a player might want to spend her money on, given her current wealth.
If a magic item is 1/3 of her current wealth, she can have 3 magic items, and then be broke. If there's a magic item she wants that costs 1/2 her wealth, it has to compete with the other possible things she might spend her money on.
Prices are competitive because every possible purchase means
not buying something else.
I think you're already on board this, but just to be sure: maybe you get your +1 sword at level 6
and then never again upgrade it?
I'm really struggling here. Maybe an example would make it easy for even idiots like me to understand?
At this stage I don't understand why you would want to complicate things. Maybe when you first encountered the price-as-level idea you thought it too was complicated and thus you spontanously came up with alternatives?
Let me assure you I think level-as-price is just as straightforward and easy as fixed gold prices - to me there is no complexity issue to solve.
I am not saying this to discourage you from explaining. I am saying this to let you calibrate your expectations: I really don't need an alternative to simple gold prices (expressed as curve-independent levels), so if that's what this is about the maybe you can start a new thread to discuss that?
Of course your idea may be so much bigger than that!
There's various issues that come from different directions.
First, saying that something costs 1/3 of a given level (say, 8) is isometric to saying it's worth some fraction of the effort available from the tier. 1/3 of typical level 8 would be 4800 gp, which is about the same as 25% of tier 2. You're not actually gaining anything number-wise by choosing one method or the other, which means other considerations have much larger weight in choosing the methodology to use.
Second, it's much harder to identify which exact level an item 'should' belong at, than to identify which gaming tier you expect it to come into play at. A +1 sword is tier 2; I don't think there's any real argument about that. However, is it a level 5? Level 6? Level 7? Level 8?
Third, using the fraction of a tier method gives you a better idea of how far into the tier the player must be before they can afford the item, and also how much of the totality of what they can afford during that tier you're using up. When you say 1/3 of level 8, you really have no such gauge. How much more would the character be able to afford at level 9 if he spends all his money at level 8? Is it enough to pay for a level 9 item?
Which actually leads to another perception problem. A player might think that a level 9 item is something that could be afforded based on what he expects to earn at level 9, even if he was broke at the end of level 8. This is not the case, as a level 9 item would cost about 6000 gp, while players are only gaining 3400 gp per level during this range. Essentially, by defining a level for the item, you're defining expectations about when it's reasonable to acquire, even though that's not really the case.
Further, a level 8 or 9 item could be afforded at level 6. That's relatively easy to identify when you use 25% of the tier as the cost basis, but not so easy when it's some fraction of level 8.
Basically, you're setting expectations and perceptions that do not correspond to the actual design intent. This is the largest aspect of what I feel is problematic with using this approach. Not that the levels might not be useful to have (for example, a magic item that mimics a level 4 spell probably should only really come available after level 7).
When it comes to getting an idea of what certain things should be worth, the question on my mind is "what do we want our adventurer to be able to afford?"
The questions I have when stocking a magic shoppe include "when - at what level - do we want to introduce this specific magic item? when should it be a premium item and when should it become common-place?" and "what are good fun choices to put to our players? Which items should they have to decide between?".
While I definitely agree with the intent, and can see, from this perspective, where there's value in setting a 'level' for an item, I think it should be largely independent of the
cost of an item. You're setting availability and cost using the same metric, when those are two very different things.
Regardless of what the +1 sword costs, whether you drop it in at 5th level, or hold out til 9th level, the cost likely shouldn't change. But maybe you're pricing when an item 'typically' shows up. Maybe a +1 sword, on average, shows up at 7th level. The 1/3 estimate would price it at about 3500 gp. That's actually possible to afford at 5th level, though you'd be broke after buying it. It also roughly matches the 20% fraction of a tier cost, which is fairly close to the expected value of the sword's benefits. It's
also about the estimated price of a 1d12 weapon from my first exploration of the pricing, though that's likely just coincidence.
So..... It actually fits pretty well, from all metrics, but: Why level 7?
And now I think I can explain it in a way that makes sense: It's the level by which you could
comfortably afford it, even with price pressures from other needed items. It's not the level it's 'appropriate' to, or the level that's 'required' for it (though some items might use that, such as a broom of flying needing to be at least level 5, to correspond to the spell Fly). But it's the level that the item will almost certainly be acquired by, if the player has any interest in it.
Overall, I think the two methods complement each other. Though I've argued in favor of the tier-fraction method, it seems it would be best to approach the pricing from both ends, rather than just one.
The fraction of a tier method allows better 'objective' measures of value, tier-setting, and an idea of how much of a player's total wealth is being taken up by acquiring this item. The level fraction method allows you to set expectations of when a player is likely to acquire an item, allowing easier adjustments of when you would make the item available in shops.
So you might proceed as: A +1 weapon is worth about 20% of a tier, and should come online in tier 2. That puts the price point at an "expected level" of 7.
Aside: This would be for a +1 weapon that is still mundane (ie: masterwork, not magic), in my view. A +1 magic weapon would likely be 25%, which would be 4500 gp, which gives it an "expected level" of 8, though it's still possible to afford it by level 6.