I have three S1's running 24/7, with a combined work factor of 540 GH/s.  Exclusive of power my 24 hr ROI from pool mining is approx 0.003 BTC.  Not bad for a 1,300 USD investment, but not likely to make me a viable business entity any time soon.


A viable micro business plan would look something like this:

At current difficulty you need at least 20 TH/s to average 1 BTC per day.  Assuming you pick up used Antminer S1's off EBay and over clock them to 200 GH/s, that hash rate will cost you 300 USD X 100 = 30,000.00 USD.  You will also need power supplies, switches, cables, etc to get everything up and running; again going to EBay, that's 300 USD X 50 = 15,000 USD for 800W power supplies and another 1,000 USD for switches, PCI and Cat5 cables.

Ok, you've spent 46k on hardware, now you need a place to put it  Retail space in a scary part of town will cost you maybe $5/SF/Year where I live, 4,000 USD per year for an 800 sqft storefront.  The commercial rate for power is $0.07/KWh here, so your 40KW mining array will cost you 24,500 USD per Year.  Then there's the difficulty factor increase: plan on adding a TH/s of capacity every quarter to stay in the game, an annual cost escalator of around 14,000 USD.


Bottom Line:
46,000.00 USD initial investment + 42,500.00 USD recurring costs;
est. annual income of 209,656.00 USD at current exchange rate (574.00 USD per BTC);
minimum exchange rate for positive cashflow = 129.00 USD per BTC (at 10 yr amortization of initial investment).