Auction for John Lennon's Sgt. Pepper album cover sketch

The owners of John Lennon's former home found an old sketchbook containing this tiny sketch of the Sgt. Pepper's Lonely Hearts Club Band album cover. It's up for auction with an estimated selling price of $40k-$60k which seems oddly low for such an artifact. From Julien's Live auctions:

An ink on paper sketch by John Lennon of the Sgt. Pepper's Lonely Hearts Club Band album cover with Lennon's handwriting of the album's title on the central bass drum in the image. The drawing was found in a sketchbook left in Lennon's former home, Kenwood in Surrey, England, and recovered by the new owners. The design of the album cover is known to have been executed by artist Peter Blake based on drawings provided by Paul McCartney. All of The Beatles contributed to the design of the cover in some way. It is unknown how this undated drawing figures into the history of the album cover and Lennon's involvement.