cheapest and easiest way:
tape deck-line out to computer line in
use goldwave or a similar program to record the audio as a .wav file. save it, burn it to a cd. there's ways to clean-up the audio, but i never took the time to learn any of that. sometimes i would raise the volume a bit, but thats all. just a raw, analog transfer to cd.
im sure there are other/better ways to do this, but thats the simplest/cheapest way i know.