Goldcorp bought the project from another company (Andrean), but the number of outstanding shares of either company is not relevant. What is relevant is the total value placed on a project with a certain number of ounces. Goldcorp paid $3.6B for what was then a reserve of 2.5M oz, or about $1440/oz. That figure is very high for gold in the ground, and even with the increased reserve numbers, it's still $765/oz. Previous numbers for buyouts I have seen have been a fraction of that. But it illustrates that majors are now willing to pay big bucks to keep up their reserves. You might also expect a premium for reserves in a safe jurisdiction (US), close to infrastructure, and in a previously mined area in a mining friendly area.
Once you know the buyout number, then you just divide by the number of shares to get the price per share. SFMI and GHDC combined have less than a billion shares, so every billion in a buyout is around $1 per share. At $765/oz, that's $1B for every 1.3M oz, or $4B ($4/share) for 5M oz, the minimum estimated by the Idaho Bureau of Mines. These seem like crazy numbers considering we're now under .04/share, but they are entirely feasible if the drilling results are anything like expected.
