Magic Item crafting question - 3.5/Pathfinder

[RLFHOG3]

So I've got what could be considered "basics" of item crafting down. So no need to tell me how to craft magic items.

The question I do have concerns advanced techniques of crafting: items with multiple abilities on them.
The following will use the example provided in the core rules, the ring of protection +2 enhanced with the ring of invisibility powers.

So lets say I now have this ring of protection +2 conferred with the ability to grant invisibility as a ring of invisibility does. How much will it cost to upgrade the protection bonus from +2 to +3 and beyond? Is the increase in protection bonus considered an "additional ability" because its added after the invisibility is added or because the protection was there first, do any upgrades to it benefit from costing the normal amount as if the ability to become invisible was never there in the first place?

[RLFHOG3]

bump for a hopeful answer

[papr_weezl8472]

The +2 Ring of Protection/Invisibility costs 32k gp (20k for the more expensive Invisibility effect, and 1.5x the cheaper 8k gp +2 deflection).

Upgrading it to +3 would cost 15k gp (the difference between a +2 and +3 ring, x1.5 as it's added on to another effect), for a total market price of 47,000 gp.

Once we bump it up to +4, though, the deflection bonus is the more expensive part of the enchantment. The price of a +4 Ring of Protection/Invisibility is thus 62k gp (32k for the +4 deflection, and 1.5x the 20k for Invisibility). A +5 ring would cost an extra 18k, for a total of 80k. If you're upgrading from an existing ring, the upgrade cost is just the price difference between the new and old rings.