I don't see the connection with $250.
DeathAndTaxes is very good at math.I really like his posts.
For example 65 million difficulty gaining 75% per month for a year results in 50 billion difficulty. The electrical cost even at 1W/GH and $0.10 per kWh would >$250 per BTC.
This is actually pretty funny. The basis of a currency is how many resources must be wasted to make it. I like.