I bought a Sony MZ-R30 in Germany for DM 590.- but living abroad you can export it and get 15% back so finally the minidisc costs ONLY $280 (1 US =3D 1.80 DM) which I think is really inexpensive for such an amazing technical wonder. I fully agree with all the minidisc enthusiasts!
However one thing really bothered me, the optical fiber cable costs about $40 which is about 14% of the R30, which makes no sense to me (somebody is making BIG profits here). For my home unit I already had an optical cable (MONSTER brand) which connected the CD player and the JE-500. However, these connectors don't fit into the R30 because it has the combined analogue/digital input which only accepts the optical miniplug (also $40 for the cable).
So I found a cheap solution: for a few dollars buy an optical fiber cable at an electronic surplus store (3 feet or so or whatever you want). Also buy a 3.5mm phone plug at Radio Shack (part no. 274-284C). Pull out the innermost connector of this plug and replace it with your optical cable. Since my optical cable was smaller in diameter I wrapped some tape around the fiber cable so it could be inserted nicely into the tube of the phone plug and remain centered. By first inserting the plug into the R30 you can carefully insert the optical cable until you feel that you can not push it in much further. Now clamp the cable as you would with a regular electrical cable and screw on the connector cover. Don't forget to feed the cable through the connector cover before you insert the cable into the plug. Now you have to insulate the outer part of the 3.5mm plug (with Scotch tape or some other wrapping) and everything should be ok.
If you did everything right (no signal source connected so far) you should see the text NO SIGNAL displayed when you switch your R30 into recording mode and the insert the new plug.
The other end of the optical cable is still loose. To connect it to the MONSTER CABLE optical plug I simply used a matching shrink tube to connect the two cables. Remember, as soon as you see red light coming out of the cable (at the modified phone plug) everything should work.
Having learned all this I feel stupid that I even bought the first $40 optical cable instead of building my own for a few bucks. I hope it works for you too and if you want you can drop me a short note to tell me how it went.
And if you like you can donate a part of your savings to a worthy cause. How does that sound?