I know that a weapon enchantment caps out at +10 or 200K GP value. But what about skill increasing items? It seems pretty cheap to get a +10 ring of Jump. (10,000 GP)  

I remember reading something in a forum somewhere where pre-epic skill boosts can be up to +30. Is this true? After that is it just a x10 price jump or am I missing something? Please provide book title and page references so that I can support this crafting attempt.