I have bought glass panels form Gillman Ace Hardware it’s on Milwaukee ave, almost in front of Congress Theatre. The glass that I got from them was for baffles for my Sump.
just a heads up it’s an Old School hardware store.The inside of the store isn’t pristine like other places, but the Customer Service is Great. I can’t remember but I think it’s cash only.
I got 1/4" Glass from Tim's Glass and Mirror out here in Arlington Heights for a bit under $10 a square foot. Most glass and mirror shops in the area are pretty similar in price, but edge polishing can get expensive. I'd just call around in your area.