This gist tries to come up with a back-of-the-envelope estimate for how much it costs a miner to create larger, rather than smaller, blocks. An economically rational miner will only include transactions with enough fees to cover the cost to the miner of processing the transaction.
I hope this analysis helps solo miners and mining pool operators to reason about their transaction fee policies, and helps them estimate their 'charity cost' if they decide to include fee-free transactions in the blocks they create to promote more use of Bitcoin.
Uncertain numbers in this document are rounded to one digit of precision; this is meant to be an order-of-magnitude estimate; when I say that 100K of free transactions costs about $1, you should assume that the real number might be anywhere between 10 cents and 10 dollars.