Polymorphing Custom magic item

[GLPredator]

So I am trying to figure out how would I craft a magic item that would allow me to basically polymorph at will. From what I understand it would be :

Spell Effect: Use-activated or continuous Polymorph = 4 (spell level) x 7 (caster level) x 2,000gp x 2 (minute /level duration) = 112,000gp .

Now this is my question, the concept of the item would be to basically make it sort of a supernatural ability that would allow the user to Polymorph whenever needed. The goal is to basically have the item with unlimited uses per day and be able to use this as a day long thing by the usage of the Persistent Spell Feat. I would like to be able to use this magic item to polymorph what would seem at will. Very similar to how a Druid can Wildshape so many times per day, but in this case being used by a magic item at virtually unlimited amounts of time. I can imagine that crafting the item with a continuous effect would allow me to turn on and off the item at will correct?

I would really like some insight on this, if possible. Would having the item made with a continuous effect virtually make it have unlimited uses per day? I envisioned the item basically being a sort of necklace or similar item that could have like a command word or turning knob so to say. Once this is done you would be able to polymorph into the desired creature/monster.

I used http://www.d20srd.org/srd/magicItems/creatingMagicItems.htm as my guide for creating the magic item, but I feel like I left something out

I am wanting to know if I have done the calculations correctly or if I am forgetting something.

[awaken_D_M_golem]

Close on most things.

4*7*2000= 56,000 gp
and that would get you unlimited uses
regardless of how long any 1 was used.
This is probably what you want to do.

Sticking persist metamagic (mm) on there
... is much more complicated.
(4 + mm) * (7 + mm) * lets say 400 = ??
1/day times 5 = your cost/benefit crossover
You and your DM wanna hash this out?

Spell + something = (sp)
then going:  (sp) + something = (su)
These are quite out into T.O. land.
I know a few like Dweomerkeeper
but they aren't Item based.  It'd be
very Very expensive, regardless.

[GLPredator]

What about this cost?

If a continuous item has an effect based on a spell with a duration measured in rounds, multiply the cost by 4. If the duration of the spell is 1 minute/level, multiply the cost by 2, and if the duration is 10 minutes/level, multiply the cost by 1.5. If the spell has a 24-hour duration or greater, divide the cost in half.

That is why I multiplied it by 2, I dont feel I would need any metamagic feats on it since the item would be a continuous effect. My Artificer can do this if needed anyways. The vision of the item is to have it sort of a supernatural ability type of thing where my character can polymorph as needed without having to worry about daily uses or length used.

Very, very expensive is not an issue. At my level my character has just over 600k gp.

[awaken_D_M_golem]

Oh right, well it's custom anyways,
so you can make it with a shorter
duration, which'll ditch that extra cost.
And since it's continuous use
the duration difference won't matter.

Here's a psi-X Polymorph item :
http://www.d20srd.org/srd/psionic/items/universalItems.htm#skinofProteus
... and it's priced without the duration up-charge.

[PlzBreakMyCampaign]

Polymorphing into anything throughout the day very, very powerful and broken when you start making whole armies. One PC polymorphing into one set form (a la alternate form) isn't.

If you want the more balanced of the two see phylactery of change (A&EG)

[GLPredator]

Entire armies? I actually never thought of that. I actually just wanted to have it to polymorph myself and no one else.

[phaedrusxy]

Just use the Skin of Proteus. It basically does exactly what you want, for 56k.