Ethan,
I'm partial to my Ghetto Hoophouse(TM) mode of construction, using
short sections of 2 x 4's to make the main hoops. You still need 8-
footer dimension lumber for the horizontal bars. Construction scrap
may be an option.
http://www.biodiversecity.com/GhettoHoopsV2.0.html
You can add a second layer of skin for better insulation by applying a
3" foam piece over the wooden hoops, then stretching the 2nd skin over
that.
The difference in cost between wood and stell hoophouses (see Polytex
catalog for example) is hundreds, versus many thousands, of dollars.
Important for those of us living on ghetto wages, hence the name.
For power, I'm studying the idea of using my Air 403 wind turbine,
used at many Burning Man events, as a power source to charge batteries
for DC vent fans, small DC pumps, and the like. Otherwise, most people
still have grid access, which is good I guess.
Bobby G