ISO - Puzzle board (makeshift is fine)

I couldn't find the actual ISO thread - what happened to it, anyway?

But here's my ISO - Looking for a jigsaw puzzle board (could just be a piece of foam core or other rigid poster board) that is at least 26.5" on its shortest side. I can't find anything under $70 for actual manufactured puzzle boards and foam core is sold in packs of 10 or more so also gets up over $50 for this size range. We just want one piece (or two perhaps) and willing to pay a reasonable price.  (We received a round 1000-piece puzzle that is 26.5" in diameter and doesn't fit on any of our boards and it's going to be HARD, so we really can't put it on the dining room table for that long.)

There are single slabs of large foam board at Home Depot for $13-$25. 

https://www.homedepot.com/p/R-Tech-1-in-x-4-ft-x-8-ft-R-3-85-Insulating-Sheathing-320821/202532854

https://www.homedepot.com/p/Owens-Corning-FOAMULAR-150-1-1-2-in-x-4-ft-x-8-ft-R-7-5-Scored-Squared-Edge-Rigid-Foam-Board-Insulation-Sheathing-88WD/202085958

https://maplewood.worldwebs.com/forums/discussion/mol-in-search-of?page=next&limit=3210#discussion-replies-3514170