A weird one: Cyrite from PGtE (p 117) is listed as a special material, but implies (when describing the Hardness and HP of the material) that it's a modification you can make to a given metal (which gives you a +1 resistance bonus to saves vs. spells and SLAs for armor and shields, or allows you to bypass DR/magic on weapons). It's pretty cheap for weapons, too - 250gp is very affordable.
A Dwarvencraft Cyrite weapon actually compares quite favorably with a more standard +1 weapon - it's a bit more durable, has the same bonus to attack rolls, and doesn't have a magical aura. Plus, it only costs 850gp over the normal cost of the weapon - that's an absolute steal.
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Also from PGtE, on page 23 there is the Bloodtouched Rite, a ritual that the Blood of Vol performs for people who have impressed them. You drink a bunch of blood, permanently lose 2 Con, and gain the following:
+Cha to your HP.
A +2 Profane bonus to saves vs. a lot of things.
+1 to your CL for Necromancy.
+1 to your effective Cleric level for Rebuking.
These benefits are free (I mean, you lose the benefits if you get rid of your Con score, but still). If you're in an E6 game, you might not even notice the drawback if your Charisma is high enough.
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EDIT: Oh, yeah, and I just noticed something about the Beauty's Bounty feat from the old Fey web enhancement. It gives you +1 HP for each point of Permanent Charisma you gain. It's still pretty crappy, but it's a bit interesting.