skelso said:
Thanks for all of the good advice, everyone!
What if I calculate it like this?
A 4th level scroll costs 700gp. An 8th level scroll costs 3000gp.
So, if I take 2000gp, divide it by 700gp, then multiply by 3000gp, I'd get a price that's the same factor larger as a Dimension Door scroll compared to a Quickened Dimension Door Scroll (though I realize it's not possible to make a quickened scroll.)
That amount comes to 8571gp, which I'd round to 9000gp.
Does that seem reasonable?
I don't think a formula is going to help you - what's it mean, after all? You're best of judging for yourself what is a reasonable price based simply on other similar-priced items and based on other items with a similar function. That's the trade-off a player will make, after all. Given the vanishing property, the bolt shirt and other examples, you need to ask yourself, is this property better or worse?
Another example: the boots of swift passage (5k) allow teleporting 5/day up to 20 ft. (and need line of sight) as a move action. Note the price increase despite the (significantly) weaker effect. The Aporter Armor property adds 20k to the armor price and allows, 2/day, an 800-ft. non-line of sight dimension door as a standard action...
Maybe something like the boots of desperation are good enough, which are swift activation, function only if you're at or below half-hitpoints, and add +30ft speed and +5dodge bonus to AC vs. AoO's 3/day for 2.8k?
Swift action teleportation is valuable. Teleportation distance is valuable. A player in my campaign has the vanishing property, and it's useful at 8k. The boots you're proposing function potentially multiple times per day, without any requirement to hit first - but on the other hand, they're slotted. Still, the requirement to hit is pretty harsh, and certainly more of a drawback than the slottedness. The increased flexibility of allowing potentially multiple teleports is valuable too (perhaps a factor 1.5 increase?). That is, the proposed swift action boots should be at least twice, but more reasonably 3-4 times as expensive as the vanishing property.
Blargney's estimate is safe. I'd use that. You could let em go for something like 20k, but then they might outshine other loot the player gets of a similar price. Compared to other items of 20k, they're very good for almost everyone in almost all situations. Compare to a Beholder Crown, a Bone Ring, a crystal mask of insight, a scarab of stabilization, gwaeron's belt (21k) and others. Also, consider that the ability you're proposing remains useful even at high levels.