According to this, a gas price of 3.5 €-cent/kWh results in a price contribution of 6 €-cent/kWh for a modern gas-fired plant. Taking into account older plants, let's assume a multiplier of two. According to the diagram below, most of the variability in consumer gas prices (violet line) originates in the import price at the border crossing (green line), so that should be true for gas for power plants, too.

This would mean that from 2004 to 2008, gas prices increased (rough estimate) 1.5 cents, thus the price of gas-fired power plant electricity increased 3 cents.

_{*Lunatic*, n.
One whose delusions are out of fashion.}