Construct modification cost

Question

When using the modifications listed under Building and Modifying Constructs, are the costs of the modifications, the price you pay to craft it, or to purchase it? IE: Construct armor has a cost of 35000, is that the price to craft it? which would mean you would pay 70k to purchase that modification, or is the price to purchase it 35k, meaning it is 17500 to craft?

I have also noticed a discrepancy on the animated objects page, where it states

"He must then spend an amount of gold on reagents—to determine the amount, add the animated object’s HD to its CP, and multiple the total by 1,000."

Yet goes on to list the price as (cost of object + [(animated object’s HD + CP) × 1,000]), and the creation cost, as 1/2 the price. This all seems very contradictory, and makes it hard to determine which is the intended price for the construct modifications.

Answer 1

In the Construct Modification rules, we can see (emphasis mine):

Performing modifications on one's own construct requires the Craft Construct feat, and the creator must pay any additional crafting requirements and/or costs associated with the modification. Completing a modification requires 1 day per 1,000 gp of the modification's base price (minimum 1 day).

So adding a modification costs the amount listed when using craft construct to add it to your construct. Whether it increases when purchasing a construct with that modification is unclear, but imo it would cost twice as much, ask your GM for their own clarification.

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The discrepancy for animated objects has nothing to do with construct modifications and seems like an issue with the writing of that text, which was originally from an AP book. Instead, you should ignore that section and use the price for them set out in Ultimate Magic (pg 112), listed in this table on d20psfrd.