What are the createion rules for limited use items?

[Dwarmaj]

For a Cloak of Improved Invisibility I calculated the following costs.

Unlimited Imp Invis would be 4*7*2000gp=56,000
4x per day = 44,800
3xper day = 33,600
2xper day = 22,400
1xper day = 11,200

Each use would last 7 minutes. (Should the unlimited version cost a bit more, seems pretty powerful?)

How would you figure the price for multiple uses, but a set time. Say any number of uses, but total duration of 7 minutes.

Dwarmaj

 

[CRGreathouse]

There's really no formula for that, but compare it to the boots of speed and see if you can work something out.

 

[dvvega]

Your calculations seem okay, however here is just a comment ...

As a rule of thumb, I disallow any mage to create miscellaneous magic items that seem to be avoiding the whole Forge Ring feat and the level 12 requirement.

Most (not all) misc items have limited power and scope. There is no cloak of invisibility, but there is a ring of invisibility. The same would go for your improved invisibility.

The cost remains the same of course, however the level required to create it drops dramatically. It depends on how much magical power you wish your players to bring to bear.

Allowing them to make a cloak of invisibility (both types) frees up a ring slot for something else equally powerful. The same argument could be used in reverse, however the cloaks in the DMG are pretty low-impact compared to an improved invisibility cloak.