I agree it is expensive the way they show it. I'm definitely not spending anywhere near as much as they are showing
. I looked at many diy designs and this one stands out for me. It seems well researched and developed with great performance.
I'm just going by the basic design. I'm using things I already have, or I substituted certain materials for cheaper easier to get items. I'm using a wood frame instead of aluminum and hopefully getting a much cheaper glazing. My foil faced insulation was way cheaper too. I will be using a fan from one of the many I already have, and come up with a controler from stuff lying around. I found 3" flex aluminum duct for cheap. My cost isn't going to be anywhere near what they list. I estimate around $150- $200 in the end, depending on glazing.