The premise of this thread is built upon a fallacy. The value of bitcoin is not dependent on the cost for mining, I dont even get how somebody could say this is the case.
Consider any other product, goods or services...the value of it is not guaranteed to not fall below production cost, it just becomes bad business when it does.
If it costs me $10 to make a sandwich that doesn't mean people will buy it from me for $10. They can go to subway and get a 5 dollar footlong.
I suggest you to read up on Bitcoin, Satoshi's white paper is a good place to start. The value of bitcoin, if nothing else, can only be derived from the cost of mining it. There is really no any other way to create a bitcoin but to mine, and mining takes processing power and electricity which cost. To compare bitcoin to a sandwich is ridiculous, a sandwich is not a store of value that is fungible, limited in production and is increasingly difficult to make.