Yes. Modern proofs, even silver proofs, can be picked up at auction for well under book. To give one notorious example : the 1977 silver proof crown has added about 25% - 33% to its price in over 30 years. "Half book" sounds a fair price, don't pay too much more than that. You think 1889 shillings are common? You should see the 1887 - commonest Victorian silver coin of them all! It was an 1887 shilling Peckris, my mistake.................. I've so much to learn