Whether or not a computer is a clone has nothing to do with the value of that computer.
Clones are merely imitations of a standard-setting computer.
Generally, you'll see the term referring to computers that run the Macintosh operating system, but were not created by Apple. That should not be your determining factor when making a purchasing decision. One thing you may want to keep in mind, however, is that brand-name computers may offer more support than generic computers.