This is a sepia-tone etching by the Western artist (John) Edward Borein (1872 - 1945) depicting a cowboy on horseback in pursuit of roping a steer. The recess that you mention in the paper is referred to as a 'platemark'. The indent is caused in the paper when the copper plate that was originally etched by the artist is inked and pressed onto the paper to transfer the print image you see. This is 'signed in plate', meaning the artists signature seen on it was also on the copper plate. The print is not signed by hand by the artist in the margin below the platemark, thus indicating the print was created posthumously from the copper plate and not during the lifetime of the artist.
The estimate is based on actual recent past recorded auction sales of comparables. Retail 'asking prices' can be higher and vary.