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Short version: Get a Single DIN system (like Hydra says).

Long Version: Original Double DIN systems (60s) were created probably to allow for the heat sinks of the older less effcient HU amps and more space consuming electronics. Also Double DIN systems were less likely to be stolen as they had poor is any resale value most were OEMed for specific car marques.

Then in the 80s and 90s Double DIN were used to allow the use of both cassete and CDs in the car. Today Music's primary format is a Hard disk (not CD) and given that today's Hard disk (backed by mordern compression altorithims) can contain so much music newer Double DINs utilize the "real estate" to provide for touch screens, DVD screens etc.. these modern Double DINs are expensive (read as above 25K).