I don't know about prices - usually everything in California is inflated.
The sound system in the base MDX is adequate, but only just. The SBP color gets pretty hot in the summer too, but it's not too bad once you're inside. Just be sure to leave a towel over the seat when you leave so the leather doesn't burn your legs when you get back.
When we took delivery of our MDX, the dealer mentioned it was ok if we put in regular (87) gas. It retards the timing a bit, so the vehicle doesn't pull quite as hard. I haven't kept track if it gets any better gas mileage compared to 91. I average about 19mpg on the highway with the MDX and 13mpg in the city.