In 1845, production of Half Dollars declined precipitously at the Philadelphia Mint to less than a third of the mintage of 1844. The reason for the decline is unknown, but in 1846, production returned to a "normal" level of around two million coins. As a result, the 1845 is a slightly scarcer date, and it is much more difficult to locate than price guides might indicate. In Mint State, the 1845 Half Dollar is really tough, much more so than the 1845 and 1846. Even so, the 1945 commands only a small premium in most grades, which makes it seem like an excellent value.
The finest example, and the one that has set the auction record thus far, is the PCGS MS64 (formerly NGC MS64+) from the Eric P. Newman Collection.