For a few quid more you could get yourself one of THESE. You can get cheaper ones which are very workable little bellows pumped melodicas with the added benefit of drone buttons. £35 or so, I have one myself though seldom field it in public but it's great fun nonetheless - HERE. I use it to accompany my Fox Jumps Over the Parsons Gate & other hunting songs and sounds just braw.

Yo Ross - there's our great minds thinking alike again! There's mains driven Bontempi on ebay right now for £22 HERE which has the chord buttons Ross describes above. As for battery life, I bought my B1 from Chester-le-Street flee market more than ten years ago and it's still got the same batteries in it, and it's still going strong. The motor does interfere with the TV though...