Using a Linux-powered SBC to control a few relays seems like mega-overkill. Sounds more like a job for a microcontroller. Getting ethernet and/or wireless hooked up to a microcontroller is less trivial than hooking one up to a Linux SBC, though.
The big problem is that although the chips are individually extremely cheap in quantity, by the time you get to the point of low-run single-board computers, it's hard to get what you want for under $100. You can only get cheap electronics due to economies of scale; electronic devices are really expensive to engineer (from a consumer's price point of view, anyway). You could easily pay way more for a development board with cheap specs than you would for a Beagleboard, which as you say has an incredible amount of processing and I/O on it (but no ethernet!). It might even make sense from a cost perspective to use a Beagleboard and a USB-to-Ethernet dongle. Or even repurposing an old laptop with a broken screen, if size is not an issue and you can find one for cheap. /* PLUG: http://plug.org, #utah on irc.freenode.net Unsubscribe: http://plug.org/mailman/options/plug Don't fear the penguin. */
