If you get a chance I'd try to get somebody on the phone. You might be able to get a rough idea of how much you'll save if you stick to dimensions within the standard sheet size vs. a custom size. I think I recall you asking about sheets wider than 4'.
I seem to remember a thread about somebody wanting to build something around 5' x 10' for a footprint. I think they found they could build two at 4' x 8' for the same price because the custom sized sheet was going to cost so much. Don't quote me on that but it was something to that effect.
Hope it works out. If you can drive to Denver and back for say $200 I'm sure that will be cheaper than shipping.
I just herd back from them, Cheapest price yet ! Looks like I will be driving to denver. Oversize acrylic sheet is not over priced but requires a 10 pc. min order