you could get a (new) USB turntable fairly cheap. plug it in your comp and go..

..or a regular (used) turntable from a thrift store for $30-40, but you'd have to buy a small pre-amp ($40?) to make the signal 'line level' for your comp...

in both scenarios though, the cartridges and needles are needed, important & expensive. The Shure M447 is widely used in hip-hop for scratching because it has low record-wear and high output. The cart+needle cost $70 to start, but then replacing needles from there on out is $30 (you keep using the same cart).

...but if you want to scratch vocal snips over the top of your beats, it helps to have a turntable that's direct-drive like a Technics or similar, and you need a battle mixer (take the place of a pre-amp, and offers more control over everything). If you want to beat juggle 2 records, or learn about mixing, then you need a 2nd turntable.

...then if you've got all that, and you want to be able to manipulate MP3's and CD's like they're vinyl, then you get Serato Scratch or M-Audio Torque or similar.

..and then you enjoy turntable bliss. You don't have to take it this far, but it's fun if you do.

btw...I've got this whole setup, but I lack an ASR-10 which I desperately want I takes a lot of $$ to build a great setup.