The cheapest I have found this unit new is £29.99, not bad at this price to monitor your electrical usage.
* easy to install - attaches to any electricity meter, no wiring needed
* three display options - choose from CO2 emissions, cost per hour or kilowatts
* real-time readings - monitor your electricity usage to the minute
* help identify savings - encourages energy saving actions by linking your behaviour to your bills
* Up to £20 savings per annum