You forgot about the fact that mining difficulty increases over time and this results in the need to get bigger mining rigs and hardware and makes it harder to acquire Bitcoin in general which leads to the price increases like we are seeing today.
i don't think that increase in cost mining bitcoins is proportionate to increase of bitcoins price.
what really amazes me is the recent volatility of bitcoin, the price is changing plus/minus hundred of dollars within single day.
I think bitcoin market is not that huge (yet), can there be some "shadow market makers" manipulating the price and making huge profits from this crazy volatility?