Comment: Some are some aren't

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Some are some aren't

The box is made of wood (any kind will do). The ridge foam insulation can be bought at Home Depot and is cheep. The reflective insulation is also cheep and at home depot. He used metal tape to finish things off and wile it is a bit on the pricey side a little goes a long way and 1 roll would be more than enough.
The real cost that I have found is the solar powered attic fan, around $300, My plan is to use computer fan that runs off a solar panel. Computer fans are 120v so I will have to put together a small circuit to step-up the 12-24vDC to 120v but i am guessing i can do that for way less than $300

I will post up a parts list with prices on the big one I am about to build.