As for your question on what hardware cost to use - naturally hardware that can be purchased right now isn't such a great deal (or everyone would purchase it until it wasn't available).  The recent bitmain usb chips are priced at $50 for 2 GH/s (overclocked) and cooling would need to be applied and the bitmain S1 is $1700 for 180 GH/s

I don't think using those prices ($10/GH + electricty) are fair for your analysis.  You can find cheaper options with a high chance of delivery if you are willing to wait until April / May - but no one knows what difficulty will be then.  If you were going to buy mining equipment today I think you'd need to get in line on one of this and gamble on the difficulty or continually monitor for the next generation (more efficient) pre-order and again gamble.