To approach this i've suggested a "House rule" to the group that leans up towards some of the info from sourcebooks like Sprawl survival guide, but moves things on to make things a little easier.
The suggestion is basically that the runners can maintain fake ID's of a given rating as usual. These are used to buy legal stuff like renting a safe house/crash pad under that ID, purchasing a car, or buying every day commodities. So far so good.
My suggestion for simplifying the process is that once the runners make money from a run, that money will usually tend to be paid out in certified cred sticks or similar. Runners will need to transfer some of that money to their real SIN'ed ID's to help maintain life styles, and to have some ready cash to flash in places where people might turn their heads at waving a certified stick around (e.g. high class establishments would be more used to peple using their identified sticks/accounts to pay for things than a ready lump sum - just like most people would pay for a new car on a credit card than carry in a suitcase full of crumpled notes today i guess).
The legal/fake ID's obviously have the added advantage of allowing potential for travel (as long as checks are passed of course), might get you out of a simple situation like getting uplled over for speeding, etc.
To facilitate the process of maintaining an ID, it is registered for paying taxes. A decker or similar can label a cred transfer for "consultancy fees, or even salary from a registered company if the runners create one (slightly further down the line in the campaign). So to make things easy, tax is deducted at the moment of transfer to the ID rather than having to mess about endlessly with annual tax returns and such like (we're not playing shadow accountants). Its been a while since i've been through all sourcebooks, but the rate i recalled from Shadowbeat was 30% income tax. I've lowered this to 25%.
So if a runner gets 2,000


The rest of runners funds are basically kept on cetified sticks, or in shadow bank accounts once they gets these established. These will of course not be taxed and can be used to buy stuff from fixers etc as usual, but they are difficult to use for legal purchses above a few hundred nuyen.
I'm interested in hearing other peoples take on this - is the tax rate too high? Does anyone have any other references of tax rates that I have missed? Do you have pointers to other systems to maintain money and idendities that work without making this element one of overriding complexity?