My memory...which is very hazy and limited on this topic...is that the Germanium based transistors have a VBE of .3v instead of silicon's VBE of .7v

So in things like amplifiers it gives you less zero point crossover distortion. In digital I believe it lends to a faster switch time but I could be very wrong on this part.

Germanium is much more rare so the cost is naturally higher...from what I know.