You'll find better deals for Casascius coins on this site than you will anywhere else. And try to remember that you're buying the bitcoin value AND the historical/numismatic value of the coin itself. Casascius was the first person to mint actual coins to hold bitcoin. The pieces are really quite important in the history of this digital currency, the first digital currency the world has ever seen. If Bitcoin remains in existence for a long time these coins will only increase in value.
There've been plenty of digital currencies beforehand. They were all centralised and murdered though.
Whatever happens in the future, Bitcoin has made a gargantuan splash. Casascius coins will have historical value even if Bitcoin dies. It'll be a historical reference for a long, long time to come.