Well, I guess it depends on how vital you want the business be in the campaign.
The easiest would be the dayjob flaw from runners companion page 103. Flavour that with "special customer requests" and you suddenly got a nice "job" at procuring that telsma from a wendigo, to sell at your talislegger shop.
But Im not aware of more indepth rules regarding shops. How specific do you want it it be? do you want it with a "real budget" or just wing it? is it for 1 player or is the whole team in charge of the business?
trust fund, made man and black market pipeline are qualities from runners companion that also might be useful, with a bit of tweaking.
It'd be just myself, so one player. 
It's really just for backstory purposes, but it kind of seems weird that I wouldn't be drawing in some kind of cash flow...but on the flip side I don't want it to be any serious amount of money (otherwise, why would I be running?).
Here's the thing of it, Most non Corp "shop" operations are probably subsistence earners. Meaning they barely take in enough revenue for the owners to live a modest lifestyle (low to middle), and pay for the general upkeep of the place (and any additional employees at a lower lifestyle then the owners) and that's assuming the owners work as well.
So, are you a shadowrunner? or a business owner?
If you are a both, then you have just saddled yourself with the Negative quality: Dayjob (choose what level for your monthly take home for the amount of hours you put in).
All done
In other words, like the sticker on my bumper says: "ASS, GRASS, or GASS!!!! NO FREE RIDES!!!"
So, no, a "totally cool" back story does not get you a extra cash
Now if you are talking about INVESTING your money into a private business AFTER the game has started, that is a different dish of turtle soup. This is the stuff that entire CAMPAIGNS have been based around!!
but there is no hard-fast rules in SR for it. Best advice? do a little research into similar private businesses and pull up investor reports.. they should give a good Idea of your return... but don't expect it to be much. Most businesses take 3 to 7 years to fully pay off the investment capital and start providing real returns.... some businesses take even longer!
Game terms: if you invested $10,000 in a business, and the GM determines that it is 3 investment return: you can expect to get a monthly payment of $10,000/36 months = ) $278. So not really worth it from a meta game sense if you are looking for a way to improve yourself short term, but could be a great way of making use of that "Super Huge" reward and make sure it continues to pay off down the road of a multi year campaign....
