abhijit, is there space below/above your current HU to add another HU? I'm not familiar with the Baleno, and that's why I'm asking.
You really don't need a switch to switch between the 2 HUs. YOu can feed the stock HU's output to the new HU's AUX in, and run all speakers etc from the new CD-HU.
A basic CD+Mp3 hu should run to 7-8K. Blau's entry level CD+MP3 is Mumbai, at about 7400/-if I'm not mistaken. You may find Pio HUs for lesser, but make sure you buy Pio only with Bill & warranty. Sony also has one HU (forgot the model) at 8K.
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