Very variant spell magic

[Varyon]

Originally Posted by Whitewings

The same laws of economics you reference. Halt Aging items would be in absolutely huge demand, far outstripping supply, which always results in higher prices. And how does the possession of a Halt Aging item do the second enchanter any good in terms of creating more?

For the last bit, Fred's likely assuming some ability to reverse-engineer an enchantment from having such an item. As for the rest, you need a significant barrier to entry for demand for a service to markedly outstrip the supply for it. There's more demand for fast-food workers than for gynecologists, but the latter have much more significant barriers to entry (namely, the sheer amount - and cost - of education required), so they are much rarer (enough to outweigh the difference in demand) and thus make more money. If it is indeed rare to find someone who is willing to teach Halt Aging, that can be a significant barrier, but by the very nature of the spell those who know and are willing to teach it would be continually increasing (they don't die of old age, and thus are likely to stick around for a good while).

Originally Posted by Whitewings

Also, an assumption of this setting is that most mages create items for use in their professions, rather than as their profession.

You may wish to bake that into your enchanting mechanics. Perhaps that 100 energy per day figure is only for personal items that are either difficult or impossible for others to use, while a slower rate would be in play for general-use magical items. The economic reality is that a healing mage could likely make far more money (and far more of an impact) selling healing wands than personally healing those who come to him with a 100 energy-per-day rate of enchantment.