Low E string buzzing

How old are the strings? Older strings ,especially nylons, are prone to this if your set up with fairly low action...That's what I would look at first as it's the easiest to fix. If it still buzzes check the neck relief as tubatooter has adviced. The neck should have a very slight up bow to it. If it's too straight or back bowed it will cause buzzing. Being a $50 guitar and a classical to boot I doupt it has a truss rod but the neck relief can be altered by changing string weights.  If it's too straight or back bowed try moving up to a heavier gauge string to add a little relief and that will probably solve the problem. If not you need to determine were it's buzzing. Fret the string in the middle of the buzzing area and put a piece of paper between the sting and frets behind the fretted string ,toward the nut, and see if the buzzing stops. If it does, chances are the nut slot was cut to deep and a nut replacement should solve it. If it still buzzes than see if you can determine on which fret it's hitting. You may have one that has started to come up or was not finished properly. In which case you will need them leveled and dressed. Also check that you have enough height at the saddle. idealy the saddle should extend atleast 1/8 of an inch above the bridge. If the saddle is too low you don't get enough down pressure on it and the string will buzz on it. Therefore you need to replace the saddle. That should cover almost any sinerio you incounter... Sorry that got kinda long   -Pix