If you take care of them (cover them when not in use, don't bang it on the ice, don't drill through/into sand/rocks, don't let anyone else use it!) they should last you many many years.
They are more expensive because the "blade" is the whole cutting head (red in most pictures). I have a spare but have never needed it in the 3 years I've owned it. The cutting edge is very very sharp. Most folks cut themselves at least once on it, then they learn. I am no exception.
They come in two varieties: with a power point and without. The power point is intended for a motor; the non-power point is for hand cranking. Though both can be used interchangeably. The power point makes it
just a bit harder to hand crank. It keeps the bit centered, and helps it start a hole. If a point breaks off I
heard you can grind off where they were welded on, and use it like a normal bit. If you were planning on eventually adding a Gator or a Tanaka, then you might consider a power point version. If you are definitely going arm power, then avoid it. JMHO.
I have owned a Gator that I used with my Nils. I now own a Tanaka.
MD