It depends how powerful your pc is. The monitor uses most electricity, so if you have a huge monitor it will cost more.
Graphics cards and fast processors also use more electricity than less powerful machines.
More info here.
http://michaelbluejay...ricity/computers.html
Hibernate doesn't use any electricity. It copies the contents of your RAM to your hard drive, then powers off. When you switch on again, it copies it back to your RAM and away you go. It's not the same as standby where it doesn't really turn off but just uses less power.