ok, there it is.

here's the text of the original post, so that you can see what i started with:
ok, i want a +1 magical dagger, with the ability to use a 7th level spell (probably at 15th level caster) either at will, or 3/day, with the trigger release on a successful attack. the pricing has been complicated, and i want to know what other people think would be a fair price for it, especially when other 7th level effects usable a few times a day are not that expensive.

target spell:

yeah, i know you're all scratching your head now. basically, i want this thing to disappear when successfully thrown at a target, and in their place, the twin weapons of the spell are summoned, pummel the target for a few rounds, and then, when the weapons disappear, the dagger reappears back in the thrower's hand (a la 'returning' property, which will be figured in later).

base cost of +1 dagger = 2,302 gp (8,302 gp once returning is thrown in)

base cost of 7th level/15 caster level effect, usable at will or 3/day = 210,000 gp (ouch) (arguable that it would 420k gp with an at will ability; though i could, by the srd, have it usable 1,000/day and still cost the same as 3/day; DM approval comes in here...).

created for a warlock/sublime character

mitigating factors: one already set in stone: spell only triggers on a successful thrown attack. others are flexible; maybe something like 'only usable in conjunction w/ martial maneuver', or 'only usable in a shadow hand stance', or 'only usable by chaotic creature', etc.

i realize that mitigating factors won't drop price a lot, but they should help.

so, base price, before other modifiers: 218,302gp for a per-day item, or *possibly* 428,302 gp for a per-hit item.

so, am i missing anything? how much do you think that mitigating factors are worth? any of you have any ideas for better mitigating factors?

realize that mitigating factors generally look pretty stupid when you already have the character in mind that it is gonna be for; "'can only be used by creature with dodge feat'. well goodness gracious, he already has dodge, so what kind of sacrifice is that?" but, pretty much all magic items that have prereqs are built like that, with a specific type of user in mind, so it at least narrows the field.

just so you can get a better idea, here's the character sheet: