What do you mean it's def. possible. Look at intels numbers they sell chips for $100 dollars, or $30 atom processors to OEMs. Now of course these guys don't have that type of volume but it's still very doable. Perfect case in point is with Avalon batch 1, they sold them for like $1200 dollars and one module had hundreds of chips on it.
The silicon itself has a cost. The cost of miner is never going to be below the silicon cost, plus cutting, packaging, testing, etc. Then you add on BOM (balance of material = everything in a miner other than the ASIC), assembly, labor, profit margin, defects.
$1 per GH/s is pretty close to the silicon cost. Chip companies aren't going to sell chips at a loss.
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So, a 300mm wafer has an area of about about 706cm^2. And HashFast's chips look like they'll be less then 1cm^2, from their renderings. You can't just divide the area by the chip size since the wafer has to be "pixelated" into chip shapes and the margins around the outside will be lost.
But, using this
online calculator we get about 600 dies per 300mm wafer.
Assuming a 10mm^2 die, you get $5000/(600chips*400Gh/s) you end up with $0.02/Gh/s
With a 20mm^2 die you get 140 chips and $0.08/Gh/s
With a 32mm^2 die you get just 58 chips and $0.24/Gh/s, which is the max on that calculator.
That's obviously not the cost of actual fabrication, of course. I was looking around and space on "multi-project" wafers for prototypes was around $15k per mm^2 with 18 week wait times.
I'd like to know exactly how much a 28nm wafer costs to actually run but it seems like you have to sign an NDA before they'll even tell you the
price.