That's if you want buying and crafting to have the same price (in other words, you think the customization ability exactly balances the need to spend spells, feats, and time to craft).
That's up to you. As long as it's cheaper than buying it on commission (i.e. fully customizable) it's up to you. Just be aware of what the effect will be, and adjust accordingly.Hmm, I'm not sure I like it: I'd like crafting being cheaper than simply buying the item