in older versions, creating magic items often required rare ingredients, instead of or in addition to the gold and XP required to create the item.
Yes, and in older editions, you actually EARNED xp for creating magic items--you didn't lose it! The idea of XP cost for a spell or magic item is boneheaded at best!
And going out on an adventure to earn XP for a magic item component only is silly. How exactly do you do that? The Fighter promises not to remember any battles or tactics used in the quest? The Rogue promises to forget about the different traps and sneaky stuff? Not only is that penalizing the people NOT involved in the making of the item, but its setting everyone back just to make something.
Herzog, its nothing against you, its the entire concept of spending XP that I've never agreed with.
If you want to do something, create something to spend, then use 'phantom' XP. If a character has earned 30,000xp from adventuring, etc., then they have 30,000xp they can use for spells and magic items and can't use more than that until they gain more xp.
That way, you don't suddenly become stupid and forget skills, feats, how to fight, spells you knew the day before, etc., just from casting a spell or creating a magic item.
You can also create magic items that supply "xp" to be used in the casting of a spell or creation of a magic item. If you don't want your guys turning into magic item factories, then just limit what they can do between adventures because they definitely won't have time for that stuff during an adventure unless you're stretching it out over days and weeks.
Jacking up the cost is a poor idea too. The cost for spell components and making magic items is so far beyond screwed up already that you shouldn't want to make it worse.