All but the highest cost ability gets multiplied.
And to calculate the price when adding an ability you first calculate the cost of the *complete* item and then subtract the cost of the previous item, which you already have.
For example:
If you have an item (ignoring affinity for now) that adds +2 Strength (4,000 gp) and add a property, which adds +4 Dexterity (16,000 gp), the lower cost gets multiplied by 1.5, therefore the total cost is then 4,000x1.5 + 16,000 = 22,000 gp. The difference you have to pay for adding the property would be 18,000 gp in that example.
Bye
Thanee