[RPG] How much do sheep cost

10g per item.

That's exactly how it works: you find and hire someone who can cast identify and they use their spellcraft skill to determine the properties of the item. (The charge is for the service performed – obtaining the benefit of a spellcasting. There's no service performed if they just cast it on themself and then sit there refusing to identify your stuff.)

Note that:

• one attempt at identifying an item using spellcraft takes 3 rounds
• the duration of identify is 3 rounds per caster level
• the cost of a spellcasting is caster level × spell level × 10 gp

So no matter how high level your NPC spellcaster is, it costs 10gp per item identified, assuming they don't fail the check (which they likely won't, with a +10 bonus due to the spell). Also, unless they're of high enough level to be able to cast multiple identify in one day and identify multiple items per casting, it may take some days to get a whole haul of items properly identified.

The trick then is in finding someone who can perform this service. Not every shopkeeper – even a shopkeeper of a "magic item shop", if you have those in your world – will be a spellcaster.

There is no simple (official to my knowledge) answer.

When magic is involved the cost is given by the magic enhancement irregardless of size. As money quickly goes into the tens of thousands, few care about tiny sized weapons base cost instead paying full price and saving time on the paperwork shortcut.

However, there are some suggestions:

• DMG has section about modifying equipment for abnormal body types, such as wings or extra arms. Its 30% more base cost. Considering the difficulty in making tiny rivets and stitching...
• Model the solution off of armor: Tiny, Fine, & Diminutive = 1/2 x Small. Large x 8 = Huge x 4 = Gargantuan x 2 = Colossal (doubles each size increment). The larger options being for material costs, while smaller requires crafting skill regardless of material savings.
• Outside of weapons: magic items (like rings) adjust to user size and have the same cost and weight. Personal items (like tents, food, water skins) adjust by 3/4th per size increment by Player Hand Book. Some items (like tools, vials, books, and rope) have a fixed cost regardless of character size, by logic and player hand book. [Huge troll climbing thin silk rope, maybe house rule that?]
• In general, the answer is always ask the DM, house rules abound. Some campaigns ignore weight in all but extreme cases. [Carrying a castle or 100 weapons.]