Is there a demand for printed feed sacks? 

Lots of people collect them. Years ago, I use to buy them for a couple of dollars. Now they go for $10 and up! There use to be a feedsack club.

Probably..  I wore clothing made out of them when I was a little girl. Everyone had them as everyone had chickens, or ducks etc. 

I think Darlene Zimmerman did a book on Feedsack Quilts some years ago.  Post them up on FB Marketplace and see what happens.

We have close to 800 of them, and we figured it would be a sin to cut into and use them. Now as we are older (MUCH) we dont want to just leave them to the kids to decide what to do with them. We know they would just be garage sale items. Some of them according to the internet searches are quit valuable. We would not be apposed to selling them.

Wow!  Sounds like they could be sold for a windfall!  Good luck!!!