> Would hit point upgrades be attached to armor, to weapons and/or armor, or to the monster itself? If they're attachable to weapons *and* armor, while figuring out the cost you'd have to assume that players would split their total number of HP upgrades evenly between both pieces of gear, to get them at lower prices.

Attaching HP to items you wear doesn't make sense, but attaching Str/Con does. Granted, attaching Str to armour or Con to a weapon seems a bit odd, but still.

Anyway, HP should be attached to the monsters themselves, in my opinion. Of course, this also implies that you shouldn't be able to sell extra HP, which adds a whole new dimension to it, as you'd need to spend it wisely.