Magic item scaling

[weckar]

So I was designing a custom magic item, and a thought occurred to me.
The base price of a command word item equals that same item with 5 charges/day. You can choose to reduce that amount of charges to make the item cheaper. Logically, though, there is no end to this scaling.
For example, let's say we made ourselves an item of command word Wish. The base price is 17*9*1800 + 5*5000*100 = 2775400GP. That's a lot. If we give it a limited amount of charges per day, however, the second part of the price halves, to 'only' 1525400GP total!
Now for the fun bit: How many charges do we need?
Let's start at once per day. That leaves us at 305080GP. Still a lot, but generally affordable to most high level characters.
Once a month, however, and you're looking at 9840GP. Actually a very reasonable price for a mid-level character or even lower. And scaling back from here to once per season or once per year actually makes it close to dirt-cheap.

Now, this is all under the assumption that the scaling actually does continue like this. I have thus far failed to find any evidence against it, but I believe the infinite wisdom of the playground will more than suffice.

Note; I took Wish as an example because it is one of the most expensive non-epic spells to make an item out of. It is an extreme example, and I plan to use this technique on much smaller scale.

[Troacctid]

The formulas you're talking about are merely guidelines to help you figure out what a custom item might cost. You can't use them to calculate the value of a custom item; you can only estimate the value. The DM ultimately sets the price.

You will reach a more accurate estimate if you use the guidelines that best represent the item's actual function. For example, an item that lets you cast Mage Armor at will is essentially just providing a +4 armor bonus, so you should price it based on the AC it provides rather than as a spell. Similarly, in this case, what we're really talking about with a 1/decade item is closer to a single-use item than an item with daily charges, so the single-use price is a better starting point; we'd then adjust it upward based on how repeatable it might be, not to mention comparisons to other items around the same price.