Thanks to Mikey, Eric, Red Ferret and Reevo for pointing me towards the Schimmel Pegasus Piano. It will cost you around $150,000, and also comes in a upright version. It's designed by Prof. Luigi Colani, a kind of blobby German Phillipe Stark who could make a living as a Giorgio Moroder lookalike if the design work dries up. Colani's finest creation is undoubtedly this awesome truck.
Anyway, Prince has a Schimmel Pegasus, and he got this company to build a full-sized motorised replica with a MIDI keyboard inside for his stage set.