The ability to calculate the energy used by your appliances can be a valuable budgeting tool. Keeping an accurate record of the power quality getting to appliances can help you determine when it's time to buy a replacement.
ECI REC sells Kill A Watt Electricity Meters that track energy consumption to member-consumers at a reasonable price. The meter attaches to the appliance and provides a direct readout of the hourly, daily, weekly, monthly, or yearly cost projections for that unit. It can also monitor voltage, line frequency, and power factor.
The standard unit costs $25.
A programmable, advanced unit with a back-up battery is also available for $30.