I have been told that my whole life by my father "unplug it if your not using it!"
I think that it's bad for things such as televisions and computers to unplug them all of the time. I only do that when there is a bad thunder storm or a power outage. You don't want a huge surge of power coming...
I don't know an exact price, but I do know that keys with the "chips" in them are more, and also if the key had a built in button box it will be a lot more. I needed an extra key for my hondai sonata and it was going to be like 250.00. It had the chip in it, but not the button box that was separate.