The one's already mentioned in this thread are the best "bang for the buck." The Axon is a bit pricey but you can do well with a used Yamaha G50 or a Roland GI-20. AXON does make a smaller version of its pitch to MIDI converter, the AX50 USB. It has no onboard sounds but has some more connectivity features than its big brother. It's around the same price range aas the used Yamaha and GI-20. Dunno if it tracks as well as the AX100, but I would assume that it tracks at least as good as the G50 and probably better than the GI-20. Might be worth looking into.