While wondering the isles at my other favorite toy store (Home Depot), I found some material to make tinted windows for model cars. It’s a waffle patterned clear smoke tint panel about 4’ by 8’, and costs over $20. Best bet is to go in on it with about 3 other guys, and to cut it in quarter sections.
There is just enough flat section in each “rib” for side and rear windows. I don’t think it is large enough for fastback windows; it’s not perfect. For standard coupes and sedans, it just may be the ticket.