so, first let me say i hate the idea of trading gold or mundane treasure for magic. i think it makes magic waay cool to only be able to trade other magic for it.
i also think that one of the things wizards would do to gain prestige among the wizarding community would be to create new spells. so, the question is this:
if a wizard creates a general unique spell for levels 1-9, what level magic item could he expect to get for it?
What would be a fair trade for unique spells of different levels? Would one wizard trading a unique 9th level for an 8th level and 7th level unique spell be fair?
I know a lot of this has to do with how much an individual wizard needs a spell that does a specific thing, but i'm just looking for a general guideline.