Another place to look is the trade fair at Concertinas at Witney on the last weekend of September. The trade fair runs on the Sunday and anyone can visit; Barleycorn Concertinas, Marcus Music and other makers and dealers have stands. You could also get in touch with a dealer who's coming - ask Dave Townsend which ones have booked this year - and ask if they could bring something in your price range. You'd certainly get the chance to try out a range of instruments in the same place.