From xonar's answers I estimate the value of a bitcoin to be about 8 €. This is the value xonar produces. Assuming that he is among the less productive miners with a small capital we may assume that the real value is a few € lower, maybe 4 € to 6 € or $5.5 to $8.5. The difference between value and price of $15 to $25 can thus be attributed to speculation.