I’m not a developer of accessories or gear for iOS devices, but I would have to imagine that much of the cost to develop the accessories would have to be the fees associated with Apple certification and the plugs and such you need to work with the docking connector. Some engineering students at the University of Michigan have developed a cool new device called Project HiJack that should make it easier and cheaper to make accessories for iOS devices.
HiJack is a little device that plugs into the headphone port of the iPhone or other iOS device. Once plugged in the thing can take the 22kHz audio signal and convert that into 7.4mW of power for anything you want to run. The students say that is enough juice to power a TI MSP430 microcontroller and attached electronics.
The HiJack can be produced in quantities for as little as $2.34 (USD) each making it much cheaper than Apple approved gear. There are already a few products on the market that use the headphone port for power and connectivity, like credit card readers. The HiJack can also communicate with an app on the device via the headphone port. You can read more in the original paper here [PDF], and grab source code and schematics for the project on Google Code.
[via Ars Technica]