25000 GP question

[Gabrosin]

This is also why these rules are so bad. (and why DMs should be careful when letting players design their own items)
+2 deflection to AC costs 8000gp. let's divide by 2 because of the restriction (only vs Evil) => 4000gp.
+2 to saves costs 4000gp. let's divide by 2 because of the restriction (only vs Evil) => 2000gp.
For immunity to charm and compulsion, I couldn't find an exact price, but it would certainly be at least 8000gp (see Mindvault).
For immunity to summoned creatures' attacks, at least 2000gp.

So, 16000gp would be a reasonable price for this item, I guess.
As a DM, I might allow it as low as 10000gp since the whole package is the effect of 1 spell (the 4 effects are "linked"), but below this price, it would break the balance of the game and become a must-have item for everyone.

I agree, and it's probably a good deal even at 16000 gp. Honestly, the immunity to charm/compulsion is the part I care about for my characters; the rest I can deal with, but I never want one of my creations to be turned against the party. But short of a super-high level item like continuous Mind Blank, it doesn't seem to be possible to obtain such blanket protection in another way.

Plus, in real gameplay terms conditional ACs are annoying, especially if they're conditional on a condition you don't always know the answer to. My current campaign recently had a character riding a unicorn, and its moving Magic Circle Against Evil was a headache for everyone and a double headache for the DM.

[Ruethgar]

Spell trap rune circle of three wishes.

[Biffoniacus_Furiou]

Regarding the recommended pricing for custom items, especially continuous spell effects, there's one thing you need to keep in mind:
"The minimum caster level is that which is needed to meet the prerequisites given."

Forge Ring has a minimum caster level of 12th, Craft Wondrous Item has a minimum caster level of 3rd. Note that this rule was added with the DMG errata, so preexisting items do not follow this, but this means rings, rods, arms/armor, and wondrous items crafted by the party have a variable caster level but a nonvariable price. This is actually one of the benefits of crafting printed items yourself in the higher levels.

A Ring of Protection from Evil would cost (spell level 1 x minimum caster level 12 x 2,000 gp x 2 for 1 minute/level duration) = 48,000 gp.

A Wondrous Item of Protection from Evil with the appropriate body slot affinity (DMG p288, amulet/neck slot, cloak, or robe in this case) would cost (spell level 1 x minimum caster level 3 x 2,000 gp x 2 for 1 minute/level duration) = 12,000 gp.

The guidelines for pricing custom magic items usually work, as long as you follow the rules for the item's minimum caster level.

[ChocoSuisse]

Yes, forgot this.
But this rule is a bit clunky too : the difference of price between a ring and a wondrous item is probably too high.
(actually, to my mind, rings should be included in wondrous items)
And with this system, a Ring of Invisibility would cost way more than 20 000gp.

[Vindicus]

Any other wacky ideas?

[Coidzor]

Any other wacky ideas?

Shax's Indispensible Haversack comes to mind, but it's not exactly one item, either.