dvvega said:
I don't know about the exact pricing, however think about the main weakness of an ioun stone.
"they spin around the user's head"
"they have low HPs and a crappy hardness"
Any creature that has a faint inkling of what magic is is going to try and whack the damn thing. A wizard will try to blast it off, and so forth.
The ring, on the other hand, is pretty well protected, especially if it's worn under gauntlets.
People underestimate the power of attacking items.
Except that you can't attack the object when the person wearing it is across the other side of the room... Can you even spot it? How are you going to determine its type, even if you do see it? From 100 ft away are you really expecting to see its colour and shape?
Or in their belt pouch, whipped out during their move, and activated.
They still aren't that easy to get rid of until it is too late. (AC24, 10 hp, hardness 5). You going to ready an action in case the enemy fighter produces a ioun stone from his belt pouch?
I for one think that they are seriously underpriced. Every fighter is going to have one, or more. I'd rather have more variety in the game.
The rings use a slot, of which you can only have two. A fighter can have seven of these stones for the price of the ring, and still afford a heavy night out on the town, with the town!
That is 42 spell levels! Look at the spells available at 6th level:
harm,
heal,
antimagic field (which he can dispel at will, so it isn't really a problem),
mass suggestion,
greater dispelling,
tenser's transformation,
acid fog, to name a few.
It stikes me that the ring costs almost 100,000 gp, which would be (Spell level)^2, and takes up one of two available ring "slots" (thus gaining a certain discount).
The ioun stone would then be 36,000 gp at the very least, in other words at least thrice as expensive! This would actually fit better with the ring's cost of 90,000 gp for 10 spell levels (2 * 6 spell levels + 18,000 gp cash in loose change)
The ring's ability to store 9th level spells is limited by access to 17th+ level spell casters, which in general must be harder to find than 11th+ level spell casters...at least in most campaigns. Once PCs reach those levels, though, this no longer is a consideration.