Funny thing about the 1973 Proof Set is that this is one that in a public auction will sometimes bring more than retail money. There's two factors. The 1973-P and 1973-D Ike's were made only to fill Mint Sets. Then there's the 1973-S 40% Silver BU and Proof Ikes which get quite a bit of attention especially the later as it is one of the keys to the set. Those four factors lead some people to believe the 1973 Clad Proof to be better than it really is.