Phantom, I will try there. I looked there once but will try again.
BapZipPow, if things don't start looking up, I might just take you up on it. I'm shooting to do all the work sometime in July, so I have a little bit of time, but I'm not sure about election cycles.
Online, Home Depot shows a 10-pack of 4x8 sheets for $110, which, if that translated to selling individual sheets in the store for $15-20 each would be great... I need to go knock on doors at sign shops, apparently.