The above question has come up in my campaign, in which a Spring covenant is heading towards Summer. A trusted local Redcap, who has done much for the covenant, has entered into a contract of sorts with one of the PC mages to create for her a longevity ritual. This will obviously take up vis. The Mercere will pay the vis for the ritual, and as much again (6 pawns) for the time spent by the mage creating the ritual. This has kicked off a big debate about the 'price of a season of sponsored research'.
Does anyone have any views on the the price of a season of a mage's time should be - most especially in vis?
Quoting the Mystery Cults book, a Verditius charges twice the vis necessary to make an item, apart from the cost of making it. So for example, if an item costs 6 pawn of vis to make, he would charge 18 pawns. They have another measure of their effort however, and that is double the vis he could extract from an aura in their season of work, in addition of the cost of the work. So it could depend in the power of the Verditius (or Mage) in question.
Keep in mind that this is the monopoly price of the best item makers in the game. I found that for that price, no-one is willing to buy anything from Verditius magi, in my sagas. But I play vis-poor sagas generally.
Usually my PCs "trade" seasons of work, but the commissioner pays the costs of the work in question. Sometimes, a little extra favour is added to the deal, for magi who can extract such prices. Like, allowed to read a book for a season, political favours, or something like that.
The vis economy really depends on the amount of vis. I don't relly know if I've playes vis-rich or vis-poor sagas. I don't think I've ever lacked vis, but then again never really used loads of it. I think all but one of my current sagas has been somewhat generous with vis.
Otherwise, the economy can be dealth with using seasons of service. If the Longevity master has to spend a season making the thing for you, he'll demand 1 season of service (or resources equivalent of this) for his time spent, and one or more for payment. Time can really be a commodity as well.
I would take a look at how much vis the magus could extract from his covenants aura if he spends the season doing this instead of creating the longvity ritual (or what ever else he is sponsored to do).
Since its probably less then 7, i would think that the deal looks good.
If he could extract 7 pawns or even more (unlikely for a spring covenant, but of course possible in other covenants), i would set the price there.