[ecomodded]

Originally Posted by MN Renovator

This might be cheaper and would have a similar result, I think. It worked for Guy Mardsen. This is what I want to do.

Building interior window insulation panels

That would work well, The costs to do each of my three 4x5 windows would be $25 @ $1.25 sq.ft
The construction would be simple enough.

The double pane window would be easy and have a higher R value then the plastic window build. It would be a two man job, windows towed behind my Car on the utility trailer. They would fit in my window openings with no modification needed(standard size opening) just require proper sealing of the windows frame with the houses window opening.
It is superior ,IMO. But I still like your idea, it could be done by someone without a vehicle / spare cash or anyone to help move/install the windows.
A good option.