[3.5] How much might this be worth?

[Frosty]

I want to homebrew up a potion that when imbibed, gives the drinker a -1 (non-stackable) penalty to Will Saves for 1 hour, no save on this effect. What should be the cost of this potion would you say?

[Raistlin1040]

Using magic item creation rules:

Your base spell would probably be Doom, which causes a creature to become Shaken. Doom lasts for a minute per level. Cast by a twentieth level caster, it lasts twenty minutes. Doom is a first level spell, so we ignore that, and 20th level caster times 50, it's going to be 1,000 gold pieces. However, a few things about this. It allows a save when you drink it (although you could rule that if you drink the potion, you autofail the save), it only last 20 minutes, not an hour, and rather than a -1 on Will saves, the penalty is a -2 on all attacks, saving throws, skill checks, and ability checks. More powerful, but only for a third of the time.

[Frosty]

What about using "usefulness" rules? If you wish for your players to spend resources buying or crafting this potion, knowing that they'd have to somehow comvince the target or force the target to drink the potion in order to gain any benefit, how much would be reasonable?

[SethFahad]

This sounds more like a poiSon than a poTion to me...
The victim must be entitled to a fortitude save in any case.

If you want to give your victim something to quaff, maybe an ingested poison will do better... reducing wisdom by 2 points and presto! -1 to will save.

Take a look at:
Striped Toadstool 1Wis/2d6Wis+1d4Int DC 11 180gp DMG
Black mead 1d6Wis+sickened/1d6Con DC 16 120gp DrMag
Praka 2d6Wis+confusion/Con over time DC 19 1,200gp DrMag
Bitch's Brew 1d4Wis+1d4Int/1Wis+1Int DC 17 200gp
Bliss Root 2d4Wis/Tashas Hideous Laughter DC 15 200gp

[The Shadowmind]

By RAW?
"The drinker of a potion is both the effective target and the caster of the effect (though the potion indicates the caster level, the drinker still controls the effect). " Pretty much worthless.

Turning it into a Will-save ingested poison, let's call it a Liquid Nightmare.
From usefulness about 25gp. About the cost of a level 0 potion, using a more general but less powerful version of Lullaby as the most similar spell. Even without the save, still around 25gp for the usefulness cost.

The price is less than the poisons SethFahad listed, but is it also much weaker than the normal poisons.

[Frosty]

Sounds about right. Something you could do in town like spiking a drink with it.