I’ve got a sawmill and have a ton of cutoffs if you want to come get some and are willing to process them down a bit. Also have sawdust if you prefer that as a growing medium. Free if you bring your own containers and load yourself.
I should be teaching a mushroom growing class this or next month with the science committee
If you attend/stop by ill give you some Hericium erinaceus and or Pleurotus djamor grain spawn/liquid culture If you want. (for free or donate to the sci committee)
Ideally, you would want your logs to be fresh cut though, So your contamination risk will be higher.