Character determining the GP value of a magic item?

[Fiery Diamond]

The Appraise skill allows characters to determine the GP value of normal, nonmagical items. Detect magic and identify allow a character to determine the properties of a magic item. Is there a way for a character to determine the GP value of magic items? Metagaming is, of course, always possible if a specific in-the-books magic item is identified. But what if we're not allowing that sort of metagaming? Or what if it's a completely custom item? Despite searching, I haven't found a way for a character (not a player) to determine the GP value of an existing magic item.

Coincidentally, this also poses another issue: when creating magic items, the character spends half the base price in crafting materials. How, in-universe, does the character know how much GP he needs to spend? It can't be a matter of trial and error just approximating out to the value listed in the books or else the first attempt would cost more than subsequent attempts, perhaps by a large margin. I mean, I suppose you could say the listed cost is if they have a blueprint and it costs more otherwise, but that's making crafting more expensive for no reason.

Now, if you're willing to completely handwave the latter matter, then it stands to reason there should be a way to do the GP appraisal of magic item value. But if there is one, I haven't found it.

Is there a way? Would you just rule that if you know an item's properties you can automatically estimate it's GP value? What do you people think?

[Vaern]

I'd say that using detect magic a character could reasonably estimate the strength, and by extension the value, of an item's magic aura.
As for knowing how much to spend on crafting, they have a formula for how much of each component they need to craft the item. They don't necessarily say "I need to sink 1,250 gp into this trinket." It would probably be more like, "Alright, so... 25 gold for this, 40 gold for that, 200 for the other thing, carry the 1 and it comes out to... 1,250. Time to go shopping."

[Learn34]

I'm not sure if PF ever reprinted this with the serial numbers filed off, but IIRC 3.5's Complete Scoundrel has a skill trick which enables Appraisal of magic items.

[Gemini476]

I think 3.5E's Appraisal just worked for magic items by default? The skill trick from Complete Scoundrel, Magical Appraisal, just lets you do a nonmagical Identify when you succeed on determining an aura with Detect Magic.
There's a similar feat in Complete Adventurer that also lets you use Appraise to identify items.

Going back to Pathfinder, though, where do the rules say that Appraise can't determine the GP value of magical items? I'm not seeing that in the SRD, but maybe I'm missing something.