Serious question:
What's the "fair price" of one bitcoin? and how do you arrive to that conclusion?
Depends on how many people use it and the average dollar value of their purchases.
that was the only approximately legit reply so far
If there was no speculation (including long-term hoarding), only use for e-payments, customers (buyers of stuff or services) would buy BTC just for payments, and give them to merchants (suppliers) or payment processors, who would then sell those BTC to other customers.
Let V be the total volume of such payments expressed in USD/day. Let T be the average time in days between the purchase of some BTC by one customer and its re-purchase by another customer, after going through a merchant or processor. Let N be the total number of coins available, and P the market price of one BTC. Then, the total volume of payments, in BTC/day, is N / T. Therfore, we musthave in we must have P *N / T = V, or P = V * T / N.
Today, N = 13.5 M BTC. BitPay currently processes ~1 million USD per day of payments; let's guess that V is ten times that, 10 M USD/day. Let's also guess T = 30 days. (Note, we are assuming that no one is hoarding, so that everybody passes the coins on as soon as pratical.) Then we get P = 10 * 30 / 13.6 = 22 USD.