Here is a picture of my grain hopper (version 2.0). It cost less than $12.00. I haven't seen anyone use a toilet flange yet, and thought I would share. The cover on the thumbscrew side fits loosely and isn't pretty, but has kept the grain from escaping.
$10.67 3" Swivel Toilet Flange (from HD)
Free Plywood from "inventory"
Free 5 Gal Water Bottle (left out for recycling by neighbor...so I did)
$1.04 New bolts for mill topside