here is another business idea that i think has merit.

ethernet appliances. streaming cams and D/A converters. Many times people are intrigued by the idea of cameras around their home or business. webcams are very cheap but the USB connection is much too limited. A small case with a quality camera, an ethernet jack, and power over ethernet for less than $150 would do very well. It'd be best if the device it self were a streaming video server. The other project is a small box with ethernet, PoE, and audio-out. You can have a home network with any number of these boxes. they'd connect to an audio amp in that particular room.

base it all on the EtherNut project. Its $150 for an unassembled board. I assume once you knew what went into one you could find a way to build it cheaper.