Hi Diki
Have a look at the Silverbird form Bohm, http://www.bohm-organs.co.uk (You only need to purchase the top) because as far as I am aware there is no other keyboard that offers so many variations, it also has a good Midi control set X 3, all of which can be easily combined. (If you talk to them nicely and flash the plastic, they may even build you a custom job)
BTW Bohm instruments are hardware updatable.

Bill