anyone with the most rudimentary wood-working skills

That lets me out, then.

You're right, though - it's not a million miles away from the instrument of my dreams! The IOMD is something that

- will play a melody and a drone (at the same time)
- is not electric
- is portable
- has a range of at least two full octaves (chromatic for preference)
and
- is cheaper than the concertina I'm currently saving up for (by selling old vinyl on eBay, but that's another story)

A melodica ticks all the boxes, if only I could be sure I wasn't going to pass out playing it. (I used to busk playing the flute; half an hour at a time was plenty.) Hence the footpump query.

JohninKS - interesting point about drones. I don't think a melodica is a closed system in that way, although not having one to experiment with I can't be sure. Certainly my little Bontempi reed organ runs the fan constantly; if you don't press a key the air just escapes.