It depends on what you mean by backing up "everything" and by what the cost of "the Earth" is to you.
If you want to make an image of your hard drive which can replace it on the spot if you have a failure, I think you'll need to pay at least $30 or so for a back-up solution such as Acronis, which has worked well for me. The price on the Acronis web site is greater than that but there are resellers providing it as a download who sell it in the $30 range.
If you are content to simply back-up all of your data, and re-install your operating system and applications from their original sources when your Hard Drive fails, then a free application such as Synctoy, available as a free download on the microsoft site, will work very nicely.
I have Windows XP Home Edition and the Windows backup is hopeless. I need some software that does not cost the earth but is effective in backing up everything on my computer. I have an external hard drive to store my backup and the total backup is not large, (about 20GB). I would be very happy for some ideas and assistance.