I've been very impressed with Sandpipers, particularly the ergonomics of the design.

They do a 3 voice D/G now, for what seems a good price- although I have not tried this model.

For something a bit different, one of the nicest melodeons I ever tried was a Loffet, "Graet e Breizh" model. They have a nice smooth action and a sweet tone and are attractive, if plain in appearance. I think his prices are very reasonable, and it seemed to me that reeds were better quality than a castanagri or similar in that price range. Definitely worth considering, though it might be hard to "try before you buy" unless you know someone with one or make a trip to Brittany!