$480 for one 4'h x 2 1/2' w. One.
Edging looks like a variant of 'shower door seal':
https://www.ebay.com/itm/271278494968
Even cheaper if you browse....Buy acrylic from Hone Despot or on the Lowes' down....better direct from a wholesaler....
I'd get down dirty and try some backer rod....thicker sheet stock less likely to sympathetically pickup but will reflect indoors really well...
If you've storm windows, why aren't you using them first? Stuff thin dia. backer around the edges...
Or...move. *G*
ND is quiet...almost 'too'.....one keeps waiting for any sort of noise. ;)