Half-day use custom magic item.

A player in my campaign is playing a vampire and wants to craft a custom item that provides protective penumbra. That part is pretty easy:

2 (spell level) * 3 (caster level) * 2000 * 1.5 (10 min/lvl duration) = 18,000gp

Now the player is asking whether or not he could change that item to have a 12h duration, once per day, instead of continuous, in order to save a little cash. The magic item creation rules don't seem to have any way to compute that in any way that makes sense to me.

Other than just saying 'no', how would you smart folks handle it?

Since magic item creation is more about "feel" than the calculations, it can get hard in these situations. There isn't really a definitive rules answer. "First and foremost, these few formulas aren't enough to truly gauge the exact differences between items. The price of a magic item may be modified based on its actual worth. The formulas only provide a starting point."

His intent is to have 100% continuous protection, regardless of how he words it or mechanically hopes to achieve it. Given that intent, along with the power of such an effect, especially for this type of character, I would stick to the 18,000gp for this item, or even increase it drastically. Around 35,000gp feels right, as not really achievable until around level 10, and more likely a final-development type of purchase. This negates one of the few downsides of a very powerful template, and needs to be balanced accordingly.

EDIT: You can always gauge how much the item is "worth" by having there be only 1 such item, and have an anonymous buyer bid against him on it. Make sure the other buyer barely wins it, then have that buyer offer to sell it to the PC at the final offer price, but only after the PC completes a favor for him (sidequest).

I'm going to rephrase the player's request: "can I save money by having my sword enchantment only apply while I am awake?"

I like that answer @Java Man. I'm not going to allow it.

This is hard to balance since PCs were never really intended to become vampires. It is a powerful template to have applied, and the daylight weakness is one of the only real downsides to it.

Other than just saying 'no', how would you smart folks handle it?

A non-restriction isn't a cost savings. They don't need the item when they sleep, so they don't get a discount.

Think of it this way. If some crafty magician decided they could make 12 hr items and charge less. One of two things would happen. The magic item price union would decide to lower the published price of the item to the lower price and make all items work only for 12 hrs OR they would tell the new magician they needed to sell their 12 hr version for the same price as the 24 hr version.

custom item that provides protective penumbra. That part is pretty easy:

2 (spell level) * 3 (caster level) * 2000 * 1.5 (10 min/lvl duration) = 18,000gp

Actually that isn't easy. That is the hard part. How did you decide to go to the "last resort" pricing model?

You verified there are no similar items?
That there are no mechanical methods to simulate the spell?

This is a powerful ability. Is it similarly powerful to a scarab of protection?

The hardest part of this is coming up with a fair price and the formula doesn't seem to be fair at 18,000 gp.

I'd allow it. Then I'd let the story take place in summer and in a geographical location that's not on the equator and then I'd laugh and laugh and laugh as the PC turned to dust in the last evening rays of the day.

Also, when looking for "similar" items look at artifacts.

There are a lot of artifacts that grant immunity to various minor things (cold, energy drain, ability drain) and this spell would provide immunity to death in a lot of ways.

Which brings us to the scarab of protections. It may have been set to have "charges" because without charges it would have been an artifact.

You might want to remind the player that that item is REALLY susceptible to a targeted dispel magic. (DC 14). I'd hate to have my character get nuked by a 5th level wizard who rolled 9 or better on a dispel check. Sure it only suppresses it for 1d4 rounds but that's a
that sunburn really hurt.