An E-12 candelabra base is considerably more energy efficient which accounts for the new designs. Compact fluorescent (CF) lamps for ceiling fans should be designed to resist vibration and to burn base up or they won't last very long, so they are more expensive than regular CF lamps no matter what base they use.

The difference in cost between a medium base and a candelabra base should not be more than 5%, assuming you are comparing equivalent quality lamps. You should not be buying them at a grocery store if you want them to last their full rated lifetime; try an electrical supply house.

Here is a link that might be useful: ceiling fan lamps