I have a Korg SP-300. It's got a full-sized 88 weighted pressure-sensitive keys and is technically portable (it's designed for band gigging). However, you need a screwdriver to take it apart and move it, and it's pretty heavy (e.g. I can carry it myself no problem, but my parents or wife can't move it without help). I say it's the best compromise around in terms of cost, portability, authentic tone/feel/appearance, and electronic features (e.g. metronome, voices, external pedal, transposition).