Not a very good idea. Better reduce consumption in other ways - putting presence detector on lamps, reducing temperature (if in cold climat) or allowing higher temperature (if in hot climate).
A transformer reduces voltage and thus power consumption in lamps and other resistive loads. This is actually using the devices below their rated voltage and will reduce their efficiency. So you do not gain anything by putting a transformer in your circuit. All you get is a dimmer life (but not necessarily duller).
Devices with a broad input voltage will not reduce power at all. They will continue pulling constant power from the mains. So when voltage goes down, current goes up. This will also usually increase losses - and nothing is gained.
Also, a transformer has losses of its own. And those losses will be present 24h and 7d all year. So they can accumulate to significant figures.
Conclusion: Do not install a transformer. Your pay-off time will be "thousands of years"
I work for a transformer company designing transformers and power supplies. And in my 10 years of dealing with it no one asked me for such a thing.
There are few ways saving on your bills apart from the obvios ones where you don't leave the lights or apliences on when not needed.
The best way to save money on bills would be to install solar panels which would be enough to run most household appliences. Here in Australia if you have them and if you produce more power than you need solar panels can be connected to the power grid and what ever goes back into the power grid you get paid for from the power companies.
It's a crazy idea to reduce power consumption by installing a transformer. Transformers can be step-up or step-down. What do you use? Step down? What for? All your appliances are running the standard power at 120 VAC and if you need the lower power in DC, you have these individual power adaptors.
If you really want to lower your power bills, conserve energy by using low kilowatt bulbs, use electric fans instead of aircon, don't leave your PC forever on, etc.
Jumpering the meter is illegal and I would never recommend.
