This shows over $200 for a 4x8 sheet of plywood, mostly in increments of 1/4". Our trim is about 3/4" thick, but a 1" board is only about half an inch thick.
http://www.boulterplywood.com/MarinePlywood_4.htm
I called a local lumbermill and they said they would come out and measure, then custom-cut boards for me. Would that cost more than two hundred dollars?