I tend to use a "quick and dirty" method specific to each group, but in every case take into account experience (average total karma earned), reputation (average of the "most reputable" and "least reputable" member), success ratio (a bit intangible in some cases when they go off mission "for a good cause" or "with reason") and expected Karma take from the job. Then I factor in "loot" they can find. Where it gets sticky is each game is different, some are high money games, some are low money worlds.
I always figure that "gang level" runners will be working for peanuts, toss them a few grand and they're in possession of more than they'll see in one place in a good long while and their "laying low" time is practically nonexistent. Low-level professionals are going to expect 5 to 10 grand on a run since they'll expect to have to lay low for two weeks to a month (giving them a "yearly gross income" between 60 and 120 grand a year). Mid-level professionals are going to be expecting 15 to 25 grand a mission, again figuring they'll be laying low one average one or two months between "real" jobs (average yearly gross income of 90 to 300 grand per year). High-level pros would be looking at 25 to 50 grand per job and expecting one to three months between big gigs (yearly gross income of 100 to 600 grand per year). Prime Runners are sky high, asking pretty much whatever they think is fair and walking off if the Johnson even thinks of balking because they're primary income is from making their own work now. Naturally how much money the GM wants floating around in the world and how tenacious they make their security and police will modify these things significantly in some cases, but again, to my way of thinking these numbers make sense, otherwise, they could make better money legitimately. Also note that the figures factor in "loot" such as paydata and crates of Predators they run across and fence or matrix scams they perpetrate with stolen commlinks, not just their Johnson's paychecks.
I've experimented in my games with "supplemental income" in the downtimes based on their total earned karma under the assumption that in-between "real jobs' they work smaller gigs and, just as they call on their contacts, other people have them as contacts; then paid them less for the missions. It works remarkably well in most cases with players willing to take less for the "main job" because they just got handed a few grand for "free" right off the bat for their "downtime work" leading to them getting less money overall. This works especially well in balancing the mundanes with the awakened since if one starts getting well ahead of the other, you can lengthen or shorten the downtimes meaning more Karma to money or vice versa without having to get a bit generous above your "usual" awards for a session.
As an aside, that idea was actually born out of a running gag by a player who, with my consent, always had "new gear" exactly like he'd had perviously. We were in the 400+ karma phase of the game and he found it amusing for his very careful, extremely meticulous PC to constantly lose and destroy his gear, cars, boats, guns and clothing doing downtime jobs and always made just enough and had just enough time to replace what had been lost or destroyed by the next run. The gag got picked up by the rigger/mechanic who would "mark" his car or boat when she did work on it and look for the mark (which was rarely ever there) the next time she worked on it. By the end of that game group he was on his 8th tricked out Westwind and gone through a nearly uncountable number of heavily customized Predator IIIs. Eventually, he added the free (since it had zero game effect) flaw "Borrowed it from Q-Branch" to his character sheet.
