For $20 get you one of these

But going to and back from magnetic or FM radio doesn't help sound quality very much...

I've made the hack considered above on an old one-piece Kenwood radio/double cassette/turntable/amp/equalizer unit.

I hacked into the wires from the play-only cassette deck, attached the wires from the cassette deck and from the RCA inputs to a selector switch and from that to the amp/eq part - for the case I'd ever feel the need to duplicate a tape.

I had no problems with noise or signal levels... YMMV though

/Michael