I've always had an issue with understand the pricing of rings, so any help would be appreciated.
Ring of Sustenance, Greater
Aura: faint conjuration; CL: 5th; Slot: ring; Price: gp; Weight: -
Description
This ring continually provides its wearer with life-sustaining nourishment and automatically oxygenates the blood and removes waste gases. The ring also fully refreshes the body and mind; the wearer does not need to sleep to gain the benefits of 8 hours of sleep. This allows a spellcaster that requires rest to prepare spells with no sleep, but it does not allow the spellcaster to prepare spells more than once a day. The ring must be worn for a full week before it begins to work. If it is removed, the owner must wear it for another week to reattune it to himself.
Construction Requirements:
Forge Ring, create food and water, keep watch, air bubble; Cost: gp
Since this is based of a Ring of Sustenance, I was thinking 3500gp for not needing to sleep at all, and adding in the no breathing, something like 9000gp for the total cost.
I'm really just spitballing the gp cost here.
The Necklace of Adaptation is in the neck slot, and that's where its effect should stay. It's one of the 'valuable' slots, and freeing that up is not recommended. If it is allowed, it should only be at a real cost - the point of limiting effects to certain slots is to force players to make real choices about what abilities to get, and easy workarounds should not be a thing.
I'd price this item at 21,750 GP. 2x the price of the Necklace of Adaptation (18,000) to remove the space limitation on the effect, plus 1.5x the less-expensive Ring of Sustenance cost (3,750) for adding the effects of two items together. This is the normal pricing guideline for multiple effects on one item.
I'd also accept dropping the price by 9000 GP if it includes a clause that you can't benefit from neck-slot items while wearing it.
As I understand it, certain effects being linked to certain slots was something that was removed in the conversion from 3.5 to Pathfinder. If we go by what you're saying, not sleeping should really be either a head slot or headband slot, and not needing to eat or drink should be a body slot. The closest I've seen is PRD in Altering Existing Items, which says that not all slots are equal (though there is not pricing rule for this). It says that certain slots are more 'valuable' than others because they are used more.
While this may at first seem as if it agrees with your increasing the price by 50% (not doubling the amulet's price and then adding 50% for the ring on top of that), looking up the definition of sustenance seems that the ring should already cover this area: "Sustenance - The maintaining of someone or something in life or existence."
I have never seen an item that made it so you were unable to use an item in a different slot. Necklace of Adaptation came out in the first printing of the CRB and used alter self (bad spell for what it does), whereas air bubble came out in 2011 and does exactly what the Necklace is doing, and it's a 1st-level spell. This to me, shows that the Necklace should be updated and by doing so have its price reduced.
If I understand the magic item creation section correctly (and I'm not saying that I am), a Necklace of Adaptation should be 2(spell level)x4(minimum CL to cast the spell)x2000gp which would be 8000gp, or if it had the 7CL the item says 14000gp. The 8000gp is fairly close to the actual 9000gp cost.
A Ring of Sustenance should be 3(spell level)x5(minimum CL to cast the spell)x2000gp which would be 15000gp (you also get the reduce need for sleep for free). This is much higher than the 2500gp of the actual ring, but it does require a week of wearing it before it begins working. Is there some price reduction for the attunement time that I'm missing?
What makes the necklace's effect more expensive (going by their listed price) than never needing to eat or drink and hardly needing to sleep?
If I used the ring as a base before adding the other things, this is what I get (I think):
2500gp (ring of sustenance, ability: sustaining a person's life)+1500gp (keep watch, 75% of actual price for similar ability: sustaining a person's life)+1000gp (air bubble, 50% of actual price for similar ability: sustaining a person's life)= 5000gp. This seemed low, which is why I, in my original post, said 9000gp.
-OR if calculating as different abilities-
2500gp (ring of sustenance)+3500gp(keep watch)+3500gp(air bubble)=9500gp. That is closer to what I had thrown out as a price.
((I just realized that the Necklace actually protects from certain effects like cloud kill and stinking cloud because they effect a creature whether or not they breath it, it does so by making those effect unable to touch the character. The ring I'm suggesting does not do this, so the wearer will still be effected by those spells. This means that the necklace still has its place and isn't being usurped by this ring, so if a character wanted the protection, they'd still take the necklace.))
The primary takeaway in custom magic item design is that the formula tables are literally the last thing to consult when deciding the cost of an item--or, indeed, whether to allow an item at all. If an item already exists that does the thing you want, start with that item, then use guidelines, your judgment, and if necessary a bit of math to figure out how to price your item with respect to the existing one.
As I understand it, certain effects being linked to certain slots was something that was removed in the conversion from 3.5 to Pathfinder.
It isn't explicitly called out in the magic item pricing table, but it is addressed in the guidelines for altering existing magic items. Guidelines such as this should generally be consulted and considered before even looking at the pricing formulae.
looking up the definition of sustenance seems that the ring should already cover this area: "Sustenance - The maintaining of someone or something in life or existence.
Thematic appropriateness takes a back seat to mechanical appropriateness when it comes to magic item pricing. If you move an ability commonly associated solely with a particular slot to a slot that isn't typically associated with that ability, you're removing hard choices that are purposely built into the system. To keep those choices relevant, take a second and third look at how allowing such an item would affect the game. If you do decide to allow it, consider making it more expensive, though not necessarily as expensive as a slotless version.
The additional ability you're looking at is best compared to the necklace of adaptation, or to a lesser degree the drowning medallion or hollow mask; it is not, to my knowledge, associated with any ring slot item. That puts it in the abnormal slot category, so give some consideration to how to proceed. Allowing it on a ring frees up a different slot for all sorts of other excellent items that would be more difficult to take advantage of otherwise. (Not being able to wear it at the same time as an amulet of mighty fists, for example, would be devastating to many builds.)
Necklace of Adaptation came out in the first printing of the CRB and used alter self (bad spell for what it does), whereas air bubble came out in 2011 and does exactly what the Necklace is doing, and it's a 1st-level spell. This to me, shows that the Necklace should be updated and by doing so have its price reduced.
The spell involved in creating an item, nor its spell level, has next to nothing to do with the cost of the item in question. An inexpensive item can have high spell requirements (see sky hook feather token), and an expensive item can have minimal spell requirements (see greater hat of disguise).
None of this should be taken to mean that you can't or shouldn't allow such an item nor that you shouldn't make it available at the cost you proposed. The guidelines exist to give an idea as to how the magic item economy was designed and to provoke consideration of what happens to said economy when you throw a particular spanner into the works. If the effect on the overall game seems positive or neutral, go for it! If the effect would be negative, revise it or go back to the drawing board.