Hardware Lumber Co (minutes from DMS south on I35) currently has plenty of 5ft x 5ft 3mm Baltic Birch Plywood available for $13 and some change. If you mention you are from DMS, they’ll likely throw a rip cut through it for free for you, since the 5’x5’ is kind of an awkward size for most vehicles.
Not shilling, just felt it was a pretty good deal (compared to Amazon, for instance…), especially for lasering activities or drawer & box bottoms if you are making such things.