Help on building an item (Planar Heart)

[Shadeworld]

Greetings Messageboards!
I am an old dog when it comes to pathfinder and I have tried a variety of things, but I have never been a master item creator and thus I come humbly seeking the help and advice of those smarter than me!

In one of the campaigns I am currently in, our party is inching our way towards level 17. It's been a long and exciting journey and now my character, Ellis, is looking to experiment a little magically. He wants to create his own plane, testing how certain cultures would evolve on such a plane with certain parameters put in place by him.
Reading up on the spell greater create demiplane, I realize it's quite expensive to make an expansive plane for a culture to develop on, so I came up with this idea for an item.
I call it the Planar Heart, or the Planar seed, the purpose would be that it stabilized any demiplane it was brought onto, as if they had been made permanent, for as long as the Planar Heart was present on the plane.
Secondly I wanted it to cast Greater Create Demiplane once per day, so here is where I need advice, good messageboard, how much would such and item cost to 'create'.
I really hope one of you takes petty on me and show me the light!

Sincerely
- Shadeworld

[Cevah]

I am not aware of any similar items. So then I look to the formulas.

Create demiplane, Lesser 7th level spell, CL 13

Create demiplane 8th level spell, CL 15

Create demiplane, Greater 9th level spell, CL 17

These last 1 day per level. While I have seen one item that had a cast 1/month, 3.5 had a limit of 1/10 days. Most infrequent items are 1/week. So. Price is SL*CL*2000/(5/(# per day)) becomes:
CDL: 7*13*2000/(5/(1/7)) = 5200 gp
CD: 8*15*2000/(5/(1/7)) = 6858 gp
CDG: 9*17*2000/(5/(1/7)) = 8743 gp

As a GM I would rule these would only handle up to the spell they were based on, so a lesser planar heart would only handle a lesser demiplane size, and lesser demiplane effects. Likewise, I would impose a 24 hour attunement process and a 1 month de-attunement process to prevent swaping between demiplanes. I would also rule that they are unable to change any demiplane traits, only keep them at whatever they were.

/cevah

[Bob Bob Bob]

I think you're overthinking it. Here's the trick. First you cast any Create Demiplane and make it permanent. You can do this with the Lesser form, even. Then you cast Greater Create Demiplane and choose to add the feature "Timeless with respect to magic". Now every spell with a duration is permanent as long as it's cast on that plane. Spells like Create Demiplane.

So the price of a scroll of Lesser Create Demiplane, 17,500 for permanency, and a scroll of Greater Create Demiplane.

[Chad Nedzlek]

"Spell in a can" items often get chucked into the party bag of holding and sold as soon as the wizard get's back to town to craft an appropriate pearl of power.

The best, and most interesting items have some unique twist. And this one sounds like it could be dripping with flavor. If the flavor "the heart can make planes", I'd probably limit it to having 1 plane a time, and it can freely modify any of the planar traits on any plane it creates. It's slightly less flexible, since it can only muck about with it's own plane, but it's more powerful too, since it can do anything without cost.

I'd also probably just call this one an artifact. A thing that is the heart of entire planes of existence isn't something one should really be buying at the corner market (or selling there to buy wands of Cure Light Wounds)... so giving it a price is sort of irrelevant. So concentrate on the flavor of it and don't sweat the price. Especially if your party is level 17 and plane-hopping, artifacts they can't sell are totally valid things to hand out.

It also means a wizard doesn't just crank these out on his summer vacation. That feels... weird for something so cosmos rearranging.