Bout to pull the encapuslating trigger, but first I need to insulate the crawl space walls.  I've read that 2-inch extruded rigid foam is the way to go, but....$$$$.  Can I realistically get away with just 1-inch extruded or 2-inch expanded foam instead?  I've already sunk like 3k in this literal hole in the ground and am not even 50% of the way done yet.

Appreciate any info.

PS doing this to combat air quality issues in the house.

John Wayne Gacy says you shouldn't shirk on the crawl space.

Lol.  I went with the 2 inch.  And lots of lye.  Got a few pigs, too.  They were on sale.