There is a manufacturer in my area that sells that board new. I get it for about $12 for a 4x8 sheet. They will even cut it into strips for me to minimize my cutting. I also found a guy that recycles the same board in black that I use for cloth that I have washed so I can tell at a glance which is washed and which is not. The black board is used for packing in electronics for its lack of conductivity(lack of static electricity). I haven't cut the black board yet but it comes in about a 45 by 14 inch size for $4 each, less if you buy in quantity.
I hope this helps.
Faith