Sometimes going back in the past can be fun! In the case of the FIRST BTC exchange price we get a big surprise!
Back in 2009, newlibertystandard was parting with their mining rewards.
At the time, this came to their asking price of:
$1 for a total of 1,578 Bitcoins!
They came to this price logic by looking at the average amount of electricity required to run their mining equipment for a year.
Back before price had a true discovery, using a way to determine the price was a simple as math from the CPU consumption and mining electricity output.
This was how some of the earliest prices for bitcoin where determined in this manner and here is the original advertisement for purchasing with PAYPAL, ironically enough!