Ok so I have been lurking a bit trying to find information on oven building. I came across this oven design Home

Its around the size I would like to make mine but the price might be a tad bit of a problem. I would imagine that insulation would not be 60$ and i could salvage some from something. The sheet metal looks a little pricy as well and i was thinking i could probably cut some corners buy using hardi backerboard or whatever for the outside. The problem about the backerboard for the outside for me would seem to be building the oven out of both. As for all of the electrical components and lights could i salvage those from ovens?

I would like to build this as cheap as possible without having to buy too much stuff. Does anyone have any input on building one this size as cheap as possible? I Believe its a 2′x3′x6

Thanks for reading.