I have not really noticed that one format is less expensive than any other. This seems to be even more true now that the agency pricing model is in place.
You can still find savings with coupons or promotions (if they are available for whatever you are trying to buy), but the coming of the IPAD seems to have pretty much leveled the playing field for pricing, and not really in favor of the consumer.
This has been my experience, I am sure there are other opinions/experiences out there.
