Hi melloror,

I'd recommend looking at a used Roland A-70, which can be had for $400-600. 76 semi-weighted organ-type keys, with almost all the controller features of the A-90 (it's big brother). Lighter, more portable than the A-90 (I have both an A-70 and A-90Ex).

You can easily expand it later by getting a used VE-RD1 piano board, which I think rivals even the new SRX piano card (and I have both).

Musician's Friend has these on clearance/blem for $500.

Regards,
Chris