Blah!
I can't *stand* XP costs, in general. They just make things hard to balance.
You can have wizards and some sorcs more powerful than the CR system is supposed to handle, really. With magic items, it's a little mitigated because the 'easter egg' for leveling up is so grand. You can make a million wands of magic missle now, but if you use that XP to level instead, you can make a million wands of wish in a few days. So it means that spending XP on magic items is usually limited to an 'essential' basis. They may make a wand of a spell they would use every day, or a ring if they'd like a certain power to compliment their own, or if the other members of the party are paying, but they won't do it much, because they'd almost always rather raise a level than make a magic item.
With classes without spell progression, or when the spells are effectively bupkis (rangers, paladins, etc.), the lure of XP-based abilities is even more so, because their future levels don't contain much that their previous levels didn't give 'em. Instead of a new level of spells, they're closer to....what, a new feat? that they could've gotten a few levels ago? Whopee.
Instead, I offer the feats for magic item creation, but remove the XP penalty and use GP limits and power components alone. At first, I imposed a maximum number per level that they could manufacture (like, a scroll may be maxed out at 25 scrolls per level, while a wand may be closer to 5, etc), but it became largely useless since my PC's never really spend that much time or effort on magic item creation when they can buy it and move on with less hassle. Works just peachy for my group, and I don't open up the whole box o' problems that comes with the other XP-expendeture systems (such as the Path books, or Mongoose's class books, or Prestige Races form Oathbound) that could be done better, or just as easily, by using feats or PrC-like things, and that open up the can o' worms of not being balanced for the actual LEVEL of the character (which should be a shorthand for the character's power-level, but those heavily using XP-investment systems can't be garunteed that a character of X level can beat a challenge of X CR)....
So blah for them!
Of course, if you have fun, fine, but I personally very much dislike them.
