Yea 200 for a piece of plastic is stupid lol I make plastic for a living can get all kinds of plastic.
I wonder if a cheap piece of wall paneling would work for the backer?
An Idea I had after spending the time and money$$$ getting a reproduction piece to fit in my car, was to just do my own next time with a material I found at the Home Depot, you should check this out. Material is 4x8 FRP board in a thickness that I think would work with a similar texture to your original, so you may not need to spend the additional cost of glue, and cloth to recover. You can go with the natural white board color, or can also spray it a color of your choice, I think a black trim semigloss would work. But either way painted or covered with material, it may be an option.