I realize the virtue is more of a broad strokes indicator of a character's life style, but I have a character concept who must buy pawns of vis from the players every season which I feel requires me to negotiate a specific amount of mp. Or, if we want to keep it 'broad strokes' we could decide that the character helps broker enough business to constitute a source of income for the covenant.
But it would still be beneficial to figure out the extant of personal wealth.
Wealthy is about free time, not a particualr amount of money, so we need to know more to answer your question. A Wealthy duke has a lot more money than a Wealthy tinker.
His status virtue is magister in arbitus... another vague status as far as wealth is concerned.
Money in Ars Magica isn't even abstracted, it's really hand-waved(because the whole thing breaks if you look closely at it). Pay no attention to the gold behind the curtain, and all that.
That said, the suggested price for vis is something like 5-10 pounds of silver.
Need a pawn a season? 20-40 pounds a year. Multiplied by the number of pawns you need each season.
I recommend having a disposable income of at least Typical(100 pounds a year in profit), maybe even Greater(250 in profit).
-Albert
Why must the player buy vis from magi?
Why are the magi interested in selling them?
Those are the two primary questions, the how much isn't an issue, really.
Good question. Usually one trades for vis in time or magical goods (other vis or enchanted devices).
"Wealthy" and "Poor" as Virtues have so little in common with "how much one makes" that it's rather amusing.
A Poor Landed Noble is still going to have a much higher income, and probably even disposable money, than a Wealthy Peasant. What that peasant has is enough money to hire help (quite possibly, his wealth is in the form of being an older man with a lot of strong sons!) and enough security that he doesn't need to be constantly working the land or otherwise hustling to get enough to eat, so he can have three seasons of leisure time out of the year. Meanwhile, the nobleman still has a big horse to ride on, weapons and armor that may be worth more than that peasant's whole farm, and a manor to live in (though the armor might be catching a bit of rust and there's never enough money to fix the draft in the bedroom). Problem is, he has to maintain that lifestyle and he doesn't have the funds. Not only can he not maintain enough servants to properly live like a nobleman ought, but he has to be constantly working his land, fighting in tourneys for cash, and otherwise just staving off complete collapse. (Serf's parma, but I think that Poor and Wealthy are even more extreme for Landed Nobles than other characters, giving them either no free time or an entire year free.)
C&G has rules for this, since a Wealthy character climbing in status becomes a Poor member of the next social class and now has to scramble to make his new position turn a profit for him.
For your magister in artibus, I'd say that he's not a lot richer than an average magister (check C&G for the actual table), but he's got solid benefices from the Church and his university doesn't mind that he doesn't teach much, so he has three seasons in which to live for himself. Have 'im spend one of those seasons teaching apprentices at the covenant in exchange for the vis he needs!
LoM p 31, nope. Saved by the parma! 
To answer the OP question, "free time" happens because your position in society is secure. If you are seen to be a miser, you might drop in ranks for not being a true christian. At the opposite end when your rank increases you might have many favors to pay back and must spend all your time behaving properly in public.
Trading money for Vis is a little weird as CrTe20 Touch of Midas creates... £300, right? (iirc, £1 = 1 farmer-year wages)
And if you add an extra magnitude, you'd get £3000 for 5 pawns of vis.
Good thing too, serfs can't afford the entire book collection 
Good to know, that section in the core had me wondering if that was a bug or a feature. So only Hermetic magi or privileged covenfolk get four free seasons?
(Of course, they pay for that by having many more interruptions than everyone else, and most savvy companions will turn an adventure into a work season. But magi usually don't have to burn seasons on exposure XP and nothing else.)
EDIT: Touch of Midas is regulated in Stonehenge (Guernicus section of HoH:TL, I think) and that's probably going to spread, because inflation=Interfering with Mundanes.
According to Covenants, ALL covenants are limited to creating two [strike]pawns[/strike] pounds of silver per magus per year magically. Or, rather, spending that much of the magically created silver, but it's a relatively minor distinction all things considered since it'd be fairly difficult to prove to a suspicious Guernicus that you only used that much of the created silver unless he feels like counting it all and magically checking it all to make sure you didn't non-ritually make any Month duration silver when you heard he was on the way.
Also, what are you talking about? Magi spend quite a fair number of seasons gaining nothing but Exposure experience. Well, unless they're absolute daredevils in a slow saga and somehow manage to fit in 10 days or fewer of xp-worthy adventuring every time they're doing a type of labwork that doesn't yield instant results. Heck, some magi, whether as punishment for a crime or, even worse, punishment for being born into the Mercere family and having the Gift, need to dedicate a season every seven years to the Order, which is kinda like being an... I dunno, Super Wealthy mundane. It's embarrassing, more than anything else, but it's still seasons being spent with no fruit except Exposure xp.
Don't have Covenants, thanks for the info.
What I mean is that they don't spend seasons doing nothing but provide for themselves like mundanes do. If they get exposure XP, they're still getting something from it (lab work, books, an apprentice). I suppose the season every seven years is an exception, but that's still a little above said mundanes.
My Magical Mercere's redcap seasons have genrally been adventures and earned much more than eve exposure.
Also, RAW is explicit regarding adventure experience, it takes a season to realize it. If you have a 10 day adventure you can do things in your lab, but by RAW you can't take adventure experience, since you are doing something other than reflecting on our adventure, and can only take exposure for the lab experience. It is a very common house rule to allow adventure experience and lab work in a season, but it is a house rule.