If by hobby greenhouse you mean the pop up plastic you will be wasting your money.
Several people on the 'Greenhouse Forum' are using a Harbour Freight GH. Around $300. 6x8. It is double walled polycarbonate. And they insulate it very well.
It is not usable in the summer because it is harder to cool being so small. It also is not very tall.
Check out the Greenhouse and Garden and Garden Structures Forum.
I manage to keep my plants in a barely warm greenhouse(38-47*).
It would be nice to have it warmer but heating is too expensive.
I only have a single layer of glass so if you used double or triple wall polycarbonate you would save money in the long run.
I also use a solar pool cover to add insulation to mine.
See 'My Page' for more pictures.
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Nice setup you have there, Cactus. It looks like a fancy botanical garden inside ;-)

Did you build this from a kit or did you design it yourself? How big is it?

I've been over to the Greenhouse forum many times. Most of the threads concern the HF greenhouse or similar ones. I'm looking for info from guys like you, who live in the area and successfully keep their tropicals alive in a kick-ass greenhouse. Thanks for the pics.

Thanks, It is a Florian 32x37. We picked up the kit in SC. Had in installed by a Florian contractor.
All the details can by found on my page.
I have a friend in Decatur who uses her Solarium to store her plants. The bananas go in the basement. Her plants actually outgrow mine by mid summer. She is more vigilant about watering and fertilizing.
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Nice Cactus Very Tropical........