So quillbreaker defense is an amusing feat, and it has a lot of potential. +20 hp for a single feat is pretty awesome! (As long as you don't care about swift actions.) However, we need an efficient way to restore these hit-points between encounters, or there is not much point.
I am looking at this through the lens of PFS, so the goal is to minimize table variation.
For comparison, keep in mind that healing 1 hp with a wand is worth ~2.7gp
The simplest option is to just replace your armor spikes after every battle. You can buy bone or obsidian armor spikes for 25 gp, and masterwork bone spikes for 325. This gives us a cost per hp of 1.25 and 16.25 respectively.
Table variation: its unclear what kind of action it is to swap your armor spikes. I can see an argument for anywhere from a full round action to days. There is some evidence that armor spikes can be separate from armor. Take a look at the Demonspike Pauldrons.
If your GM rules that armor spikes must be forged into your armor, you can always invest in armored coats. The coat costs 50gp and weighs only 20lbs. Staple your armor spikes to it and swap them between encounters.
Obsidian armor spikes only weigh 7.5 pounds, so a CL 8 oil of mending can repair them, for an efficiency of 10gp per hit point (200gp per use). Its not clear how much hp armor spikes have, but if they count as light blades the answer is 2. That means mending will almost always restore them to full health. It has to be an oil because no one is waiting 10 minutes while you wave your wand around and then roll a 2 on your UMD.
If you want to be cheeky, you can pay 5.75gp per hit point (115gp per use) by first applying a wand of lighten object to your armor spikes before using a CL 4 mending oil...
Between adventures, you can hire a level 8 adept or something to hit your spikes with mending for 40 gp. (Again, 30 if you are cheeky.)
You can also use mending paste to repair your spikes. At 25 gp a flask, this gives you one of the best hp to gp ratios. The down-side is that it takes 1d6+4 minutes to dry. I'm not sure if you have to work on it for this time or not, but mending paste is probably only good for repairs on long adventures. Likely in conjunction with method 1 or 2.
The main downside is that it only works on metal.
A caster level 1 wand of Gorum's armor gives you armor spikes for 10 minutes. This is a cost of 1.5 gp per hit point! Needs an investment in UMD and can never get more then 10 hp from this though.
If you can actually cast this spell and are level 5, There is a sold argument that the armor spikes are masterwork though since they get an enhancement bonus. Since in PFS you will have 3 adventures per level, and you will have 21 adventures after level 5. That means that each pearl of power is worth 420 hp, for a ratio of ~2.4 gp per hp.
Buy 4 or so armored coats and attach masterwork obsidian armor spikes to them. After combats in which you used quillbreaker defense, swap coats. At the end of the adventure, go home and pay a wizard to mend all your armor spikes. On long adventures, pull out your wand of lighten object and CL 4 mending oils and repair your spikes yourself.
Any ideas on what I missed or what wont work?
Can't make oil of mending, as oils and potions are limited to spells with a casting time of 1 minute or less. I like where this post is going, though!
The shadow weapon spell would be good for those who can cast it - 1st level, 1 min/level, creates a masterwork weapon.
The shadow weapon idea got me searching, I found two more interesting options:
1. Reinforce armaments lasts 10 minutes per level, so you can use it in conjunction with Gorum's armor to get masterwork armor spikes.
2. If you are willing to invest in Craft(weapon) and have access to a source of ice, you can use snow shape to create armor spikes that last 24 hours. Best of all, its available as a level 1 wand. Even in hot environments, a friendly divine caster and a jar of liquid ice can provide you the raw materials.
A Unchained Rogue at level 2 can gain access to Umbral Gear, which allows her to create a light melee weapon that lasts for 10 minutes per level. If you take the talent again, you gain access to Masterwork Light weapons, this allows you to create umbral spikes as long as you are in areas of dim light or darkness.
Umbral gear is also super useful for the rest of the gear you can have spontaneously on hand.
a mindblade magus can make a magical +1 light weapon as a standard action that cost him 1 pool point that comes back when the weapon vanish (ability talk about being droped or dismissed, from the dropped part it seem even if you drop it by being disarmed. so geting it broken should be the same of sort).
only prblem is this feat only work for non magical attacks so for low levels it's great. later on you can't realy relay on it.
a mindblade magus can make a magical +1 light weapon as a standard action that cost him 1 pool point that comes back when the weapon vanish (ability talk about being droped or dismissed, from the dropped part it seem even if you drop it by being disarmed. so geting it broken should be the same of sort).
Oooo that's pretty neat. No fuss no muss +20 hp. Downside for the straight magus is that he has actual good uses for his swift action.
only prblem is this feat only work for non magical attacks so for low levels it's great. later on you can't realy relay on it.
I am assuming that "non-magical" means "not a spell." Not that it can't block a +1 sword. Though really, this is a terrible way of phrasing it, as a pedantic user could argue that he could block damage from being on fire with his armor spikes.
the feat say "as an immediate action when you take damage from a nonmagical attack,"
i took that the same way magical attack deal 50% daamge to incorpereal creatures. that is magical weapons (or mgical attacks like ki strike of monk that count as magical and others like the draconic bloodline claws etc.) and damaging spells (and again there is seperation in spells. them who summon things that hurt do not count as magical damge. see the incorpereal errrata and faq for more). there is a rule defenition if an attack is magical or not.
and as i said at higher levels most creatures will ether have magical attacks, count as such or stirght out have magical weapons. so for low levels its nice. the higher you go it loose its grace.
I am assuming that "non-magical" means "not a spell." Not that it can't block a +1 sword. Though really, this is a terrible way of phrasing it, as a pedantic user could argue that he could block damage from being on fire with his armor spikes.
Well the fire damage isn't an attack, so that's probably okay. But yeah it feels clear that the intended reading means it works on attacks that aren't generated by magic, even if they're done with magic weapons.
A Ray spell or kineticist's blast would bypass it.Things like Twilight Knife are more debatable, although since it's a spell that creates a weapon that attacks by stabbing people I'd allow it.
Quillbreaker defense breaks your armor spikes. Not one of them, the set. You generally want the spikes fixed faster than a week too The nkight.
If you make your spikes out of Greenwood (repairs 1 hp/hour) or Living Steel (repairs 1 or 2 hp/day).
If you want custom, the Rope of Knots repairs at 12 hp per hour. A similar effect could be applied to spikes.
As to how much to repair, as a GM I would say you need to repair the same amount it prevented, i.e. 5 or 10 for broken and 10 or 20 for destroyed.
/cevah