The "on hold" industry is charging several hundred dollars for an MP3 player with the following essential characteristics:
1) Solid state storage
2) It plays MP3s immediately on power on (i.e. recovers from power failure).
3) It loops forever.
Of course, they get to do this (and have to do this) by having another 12 or so completely irrelevant features and custom plastic cases and firmware.
As MP3 players go, this shouldn't be hard. Being the type who is usually willing to spend more time and money building something myself that "costs less", I was looking at build-em-yourself MP3 player kits. Finally it dawned on me to find or buy an older MP3 player and replace the firmware. Which lead me to RockBox. I'd heard about it, so it was buzzing around in my memory. It appears now that I can save money, and have only exactly what I need.
Looking at the supported MP3 players list, my eye quickly fell onto the "SanDisk Sansa c200". I see a refurb on ebay for $30 (maybe this is rare...), and an AC adapter is available for about 8 bucks (which I'd get) although one could be made pretty easily by soldering the right AC adapter to the battery terminals.
Interested in discussion about this idea, things I'm forgetting, general feasibility, and helpful first steps :-).