Well yes, if you look at the off the shelf price if the phone, the battery looks inexpensive in comparison. But I paid $99 for the phone, so a single accessory at $65 seems a bit hefty!
I'm just a bit in awe of how much the battery costs, although I can certainly see why it would be useful. I'll probably end up getting one, just surprised at the $$. I'm still figuring out the whole smartphone thing. Seems a bit like buying a house-always a new thing to buy for it!