In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
I have not read any posts about these Conservall (brand name) type of solar collectors.
I installed these (4 - 4'X16') units about 7 years ago, they each have a 8" duct with a active damper and duct fan that is controlled by a demand stat and a micro processor at the top of each panel that says that the panel is warm/hot enough to come on.
I was concerned about tight house problem with my ICF construction and need make up fresh air and this works great.
I like this concept and it works for me.