For those of us old timers, here's an amusing shootout between a SparcStation 20 and a Raspberry Pi, including both the Pi and the Pi2 (but unfortunately not the Pi0).
For those unfamiliar with the SS20, it was a workhorse desktop in the 1990's. Early pizza-box design and pricing out at well over $10,000 at the time (according to the article, closer to $25K today). It was an awesome desktop workstation, and was seen in some equipment racks as a "cheap" alternative server platform. For comparison, the Pi sells for $20, and the Pi2 for $35.
The short version is that a computer which costs roughly 1/1000 of the price performs about 7x as fast for operations (and for the record, there is no category where the SparcStation wins). For those keeping score, that's a 7000x increase in price/performance in 20 years.