[stonedragonfarms]

Sounds like you are in Hort 301 or something...

I'd like to add a couple of thoughts though.
Perhaps before you look at your coldest growing location, you should decide what sort of plants you aim to grow: I grow in a quonset style house in northern michigan (where we are routinely below 0F most of January & Februaury), but I grow primarily cymbidiums, masdevallias & nobile type dendrobiums. The point being, I maintain a cold house (48F night temp) which requires far less heat than if you aim to grow something like Phrags/Cattleya (which I would grow in an intermediate house, 60F at night or so) or Phalaenopsis which would require even warmer night temps. The warmer growing the group you intend to cultivate, the more of an expense heating will be...conversely, if you are aiming to grow cooler growing plants in a warm climate (say cymbidiums in arizona), you are going to need to adjust for cooling expenses...
Now that you know what you want to grow, where do you aim to locate your gh? Will it be in a municipal area or outside of town? The zoning here would have been a nightmare for me to contend with; while land outside of town is more expensive by some rights, the zoning is relatively lax...there are trade offs to either...
Finally...what do you see as the time scope for the business? Do you anticipate maintaining a nursery for a long period of time...or just a few years? If you are in it for the long haul, can you build your greenhouse in stages? Most of the quonset style houses can be added to in length as needed... Alternately, if you are planning on operating for a short period of time, why buy a piece of land or the equipment? In that case I would most likely lease a piece of land and the GH as well...
Just a few more wrenches in the gears...and my 2cents.
Adam