Car Insurance Question (Multiple cars)

[theben]

Help me with some insurance cost analysis (concepts/basic guidlines are fine!)

Note:
-Multiple cars (Pretend 1 civic, 1 new BMW)
-Single driver

Info: I currently drive a regular crappy car (such as a cheap civic, corolla, etc). I plan on getting a second car and will drive the junk-o car during the winter and the "nice" car (BMW, mercedes, etc) during other seasons.

-I will have liability coverage on the civic
-I will have liability and collision coverage on the BMW


How much extra will this setup cost me than just covering a BMW for liability/collision?

Since there will be only 1 driver for the two cars, in theory the "risk" costs the insurance company must bear should be lower in a case with dual cars (1 crap-o car, 1 nice car) when compared to a situation where the driver uses a nice car year round. I fear this isnt the case. Help!