Well, the ebay auction has ended, and it apparently did not sell at a starting bid of $850, and (maybe it's just me) I didn't find a price in your linked page. Just for comparison, I just bought a Bush Hog version, NOS, which was listed at $1395. Gannon blades are expensive. I also saw a new Woods (Gill) model they wanted $2000 or so for down in Florida. Your blade looks to be in really good shape, so I would think it should probably go somewhere in the range of $1000 or so, just needs more exposure. Not too many lookers for these, people just don't appreciate how handy they are.
Oh, let me add, I'm not familiar with the one made by Hester Plow Co.; not sure if they are still in business. Can't find a web site for them. But I've seen a couple of these sold by different implement compainies, one was for sale out in Colorado (Buffalo or something). The only manufacturers I am familiar with that still supply rollover scrapers like these are Dirt Dog, Bush Hog (made by Dirt Dog), and A&B Eagle Line.