I use aluminum or stainless, about $400 for a 8 foot length of chute for the aluminum ones last time i priced them. The aluminum ones I buy will last for about 20 years though
Providing the customers doesn't try and help me by smashing it with a shovel or hoe.
Quick tip for anyone reading this, don't touch the Coalman's chutes, they are expensive and once you get a dent in them they will have a hole in them shortly where the dent is even if you pound the dent out. After that they are useless, obstructions such as patches can make the difference between the coal going down the chute and it not going down the chute. Besides that the hole will just continue to grow...
If you can get your hands on a few scraps of old aluminum siding your in business. You'll have to make something to support it because it obviously won't support the weight. If you're using rice coal the pipe idea might not work, the rice needs a pretty good pitch and it has a tendency to stick to plastic if it's wet or damp.
If you're getting it delivered all you need is the window.