1) The BEST repair is to repair it RIGHT. Like what Adam said, pull the plate amp, desolder the bad cord, get a new cord strip it and solder it on. This is the only "Right" way to fix it. This also requires the most work. It would also be a good time to consider an IEC connector so you could simply replace the cord in the future.
2) Next best would be to simply order a new cable (if necessary) make the splices and solder the wires together and use heat-shrink to cover it (remember to put the heat shrink on before you solder! countless times I have had to desolder/resolder because I forgot

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3) It's not really a good option AT ALL, but yeah you COULD twist the wires together and use electrical tape. If you do go that route, then I would highly recommend using wire nuts rather than just twisting it together without the nuts, then cover it all with electrical tape. The thing with this though, I would think that if anything bad ever happened and a house fire started, the insurance company would start trying to blame this fix as the cause of the fire (whether it was or not). So to me it isn't worth the risk.
4) Send it to an authorized dealer for repair = $$$