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The streetpilot is a bit older, and isnt compatible with any backup cameras unfortunately.
About the cheapest model that is compatible with the backup cameras is the Nuvi 50 LM. http://amzn.to/1XOd7UY
And that device is compatible with the BC 30 backup camera system. http://amzn.to/25QD0I0
That package would give you the backup camera features, a new Garmin with lifetime maps and a 1 year warranty, and would come in about the cost of a new full featured garmin model from this year. * Since the nuvi 50 is a few years old ( but new in box ) By using the 50lm which is still much newer then your streetpilot, you can get the nuvi and the camera for about the cost of a brand new new from this year.
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