You've just experienced a common problem with start ups; there's not really a way to start small. The only way to get a half-way decent price is to buy by the truck load. And I don't mean pickup truck. :sad:
If the windows are small enough, you might be able to buy scrap pieces from a large manufacturer serving a different market segment. But one of the paths to profitability is keeping waste to an absolute minimum, so your parts would probably need to be extremely short. :vs_whistle:
Good luck!