Not sure how helpful this is, but for people just getting started with armor and things, i found rigid expanded pvc foam board (aka Sintra) at a national chain called Fastsigns that does displays and signs and things...it was a 4x8 sheet for $45 bucks plus tax....don't know how the price compares to other sources, but in my neck of the woods, it was the only game in town, not to mention it seems like more than enough to handle any project