Okay, so I was trying to figure out exactly how the Lyre of Building only costs 13,000 gp.
The construction requirements say:
* Craft Wondrous Item feat (caster level = 3rd)
* Fabricate Spell (5th level spell, min caster level = 9th)
* 6,500 gp in materials
So, when I look at the Table for Estimating Gold Piece Values (http://www.d20pfsrd.com/magic-items#Table-Estimating-Magic-Item-Gold-Piece -Values), it says that "Use-activated or continuous items cost Spell level x caster level x 2,000 gp". But, that can't be accurate, because it comes out to 90,000 gp.
Then I notice that items that require a skill to use should be reduced in cost around 10%. This also cannot be right, because that only takes it down to 81,000.
Then I notice that charged items have a base cost of "Divide by (5 divided by charges per day)". Well, it has a single charge a week for the building component, and a daily charge for the attack negation effect. So, how to cost that out?
If we use the attack negation effect, the equation becomes Adjusted Base Cost = Base Cost / (5/1 charge/day) which would be 18,000 gp. Closer, but still not right.
If we use the building effect, it essentially has 1/7th of a charge per day (it can only be used once a week). The equation becomes Adjusted Base Cost = Base Cost / (5/(1/7 charge per day)), which comes out to 2,571 gp. Clearly, this isn't the right approach either.
So, I don't get it. What am I doing wrong?