I think you should look into a module rather than the entire keyboard iteslf if you're looking more for "playback features". Your cheapest route "keyboard wise for a half decent arranger is going to run you at least $750 and up. A module like a Roland SonicCell.., or even a laptop alone with the right programs would get the job done.., and at a reasonable price too.
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.